John Gwyn Jeffreys.

British conchology; or, An account of the Mollusca which now inhabit the British Isles and the surrounding seas (Volume 2) online

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dull aspect : sculpture, irregular lines of growth, and (occa-
sionally) white longitudinal lines or streaks as in the last
species : colour milk-white : epidermis not very thin, pris-
matic, and marked with numerous minute concentric striae
which impart to it a silky appearance under the microscope :
margins abruptly truncate at the smaller or posterior end,
nearly straight or slightly curved in front, expanding and
rounded at the anterior end, and very gently sloping behind
from the beak to that side : beaks small and blunt, promi-
nent, somewhat incurved, with an indentation below; they
are placed very much nearer the posterior side, which is not
one-third the size of the other : hinge-line nearly rectan-
gular, occupying about one-third of the circumference : car-
tilage yellowish, smooth, thick and globular, contained in a
triangular pit lying directly under the beak in the left valve,
and forming a cup-shaped process or ossicle at its base : hinge-
plate narrow but strong, deeply excavated in the middle for
the reception of the cartilage, which sometimes encroaches on
the beak to such an extent as to make the latter appear broken
or eroded : teeth, in the right valve rather short, leaf-like, and
diverging inwards ; in the left valve longer, and parallel with
the hinge-line ; those on the anterior side are the largest in
both valves : inside nacreous and glossy, with a plain margin :
scars obscure. L. 0-125. B. 0-14.

HABITAT : Muddy gravel and in the crevices of old
bivalve shells, from 10 to 70 fathoms, everywhere from
Unst to Guernsey. As an upper tertiary fossil it is
recorded by Grainger from Belfast, by James Smith from
Bridlington, and by Searles Wood from the Red and
Coralline Crag. Its foreign range extends from Norway
to Sicily. Malm has dredged it on the Swedish coast in
10-25 fathoms, M< Andrew at Vigo in 4, and off Sicily


in 8 fathoms, and I have taken it at Spezzia in 18
fathoms. According to Sars it is found in the post-
glacial beds of Christiania.

Clark's account of the animal is that it is " lively,
marches with rapidity, and in its course turns from side
to side, sometimes resting the shell on the ventral range
in an upright posture/' Montagu, having found it
apparently burrowing in old and thick oyster-shells, be-
lieved that it was partly the cause of the small round
holes so frequently seen on those shells. Such perfora-
tions, however, are attributable to a sponge (Cliona
celata), that fills the cylindrical tubes of which the holes
are the outlet, and branches off in every direction a
course never known to be taken by any mollusk. The
relative proportions of length and breadth in the shell
of M. bidentata are very variable. The young are more
triangular than the adult, and somewhat resemble in
shape the fry of Nucula nucleus. My largest specimen
is a line and a half long, and a third more in breadth.

This small shell has been bandied about by different
conchologists from one genus to another, and received
various names. Montagu referred it provisionally to
My a. Brown in 1827 placed it in the genus Anatina
of Lamarck, and Clark did the same in 1855. Gray
and Hanley called it a Petricola. It is the Erycina
faba of Nyst, E. nucleola of Eecluz, and Mesodesmq
exiguum of Loven. The Montacuta elevata of Stimpson,
which Gould supposed was our shell, differs in the posi-
tion of the beaks and in other particulars.

TolU'my*' fcir^t^oa^

\l-M- 3. M. FERriuGiNo'sA*,{Montagu.) N*

Mya ferruginosa, Mont. Test. Brit. p. 44, tab. 26. f. 5. Montacuta ferru-
ffinosa, F. & H. ii. p. 72, pi. xviii. f. 5, 5 a & 5 b (as M. ferruginea).

BODY clear white : mantle having its margins on the ante-
* Covered with iron-rust.


rior side produced considerably beyond the shell, and forming
a kind of frill, which becomes gradually smaller and more
even as it passes along the front of the shell towards the pos-
terior side ; it is fringed with very delicate, rather short, and
blunt filaments, which extend completely round the edges of
the valves, with the exception of a small space at the umbones :
tube consisting of a small inconspicuous excretory orifice : foot
very large and muscular, slightly bent in the middle, tapering
to a blunt point in front and abruptly truncate behind ; its
base or sole is somewhat wavy and grooved through its entire

SHELL oblong, convex, thin, rather opaque, glossy : sculp-
ture, irregular lines of growth and occasionally a few exceed-
ingly slight longitudinal scratches : colour greyish-white :
epidermis as in the last species, but it is usually obscured by
a thick ferruginous crust: margins somewhat truncate but
rounded at the smaller or posterior end, thence obliquely
slanting and slightly curved in front, expanding and rounded
at the anterior end, and very gently sloping behind from
the beak to that side, with a short ledge on the other side
which forms an obtuse angle at the posterior extremity : beaks
small, blunt, and rather tumid, not very prominent, and nearly
straight; they are placed at about one-third the distance
from the posterior end : hinge-line almost straight, occupying
about one-third of the circumference : cartilage large and
solid, light yellowish- brown or horncolour, obliquely twisted
and clasping the hinge-plate on each side, lying close to the
beaks at the posterior side ; the pit or groove containing it
slants abruptly and obliquely down towards the posterior side,
and has its walls and base much thickened : hinge-plate nar-
row but thick : teeth, in the right valve one on the anterior
side, which runs from the cartilage at nearly a right angle to
the hinge-line and so far resembles a cardinal tooth, but it
then takes a sharp twist in the direction of the hinge -line,
where it becomes laminar and is gradually attenuated to a
sharp point ; the other tooth in the same valve on the posterior
side is shorter, triangular and pointed, placed on a lower level
and parallel with the posterior slope ; in the left valve the
tooth on the anterior side is pointed near its commencement
and forms a rather long laminar ridge in a parallel line with
the hinge, the other tooth being of the same shape as the corre-
sponding one in the right valve and taking a similar direction :
inside partly nacreous but mostly of a dull hue, with a plain


and somewhat thickened margin, sometimes marked with faint
lines which radiate from the beak : scars remarkably distinct,
the muscular impression on the anterior side being larger and
much longer than the other. L. 0-2. E. 0-3.

Var. oblonga. Shell narrower, and having the front and
dorsal margins nearly straight. M. oblonga, Turt. Conch.
Dith. p. 61, tab. 11. f. 11, 12.

HABITAT : Muddy ground, from 7 to 85 fathoms, on
all our coasts. It is, however, a local species, and is
seldom found in a perfect state. The variety is not un-
common, and occurs with the typical form, as well as
with intermediate gradations. Grainger has recorded
this shell from the Belfast deposit, and Searles Wood
from the Coralline Crag. Loven and Malm have de-
scribed it as Swedish, the latter giving a depth of 18-50
fathoms ; Recluz found a single valve in the stomach of
a turbot on the French side of the English Channel ;
Lamarck mentions Cherbourg as the locality for his
Amphidesma purpurascens, which is probably our spe-
cies ; and I noticed it in M. Martin's collection of
shells from the Gulf of Lyons.

Professor Loven published, in the ' Proceedings ' of
the Royal Swedish Academy of Sciences for 1848, some
important information as to the production and deve-
lopment of the fry of this species (as well as of M. biden-
tata) ; and in the ' Annals of Natural History ' for March
1850 (2nd ser. v. p. 210) is contained an excellent paper
by Mr. Alder on the same subject, and also with respect
to the habits of the adult. My description of the ani-
mal is taken from Mr. Alder's notes. He mentions that
the specimen which he observed was taken from " the
stomach of a haddock a very unpromising locality cer-
tainly for meeting with anything in a living state ; but
the little creature on being placed in sea-water appeared
quite lively, and not visibly the worse for the uncom-


fortable quarters from which it had been extracted. In
a short time it protruded the mantle beyond the shell,
extended its large foot, and began to crawl about." And
as to the fry he says, " After having kept my specimen
for some days in sea-water, I found one morning that
the bottom of the glass was covered with a minute
white dust, which I immediately concluded would be
the spawn, and on placing a small portion under the
microscope I found that such was the case. I sub-
sequently had it removed into a separate glass with a
fresh supply of water, in order to observe its develop-
ment. Though nearly round at first, the ova soon
assumed a subtriangular shape, and about the third day
strong cilia were observed on one of the sides, and they
began to rotate very quickly. One after another assumed
the rotatory state, till nearly the whole were in motion.
After rotating for about a day, they apparently burst
the envelope, and swam freely about in all directions
by means of their vibratile cilia, and at the same time
assumed more or less of a bell- shape a slender style
or thread projecting from the centre of the ciliated base.
This organ, which has been observed in the embryos of
other species, has been described as a kind of byssus, by
which the little creature can fix itself securely to other
bodies. This, however, I did not observe to be the
case in the present instance. It soon appeared to be
absorbed ; the animal became gradually elongated, and
the cilia were withdrawn into the shell, which then
began to appear; but at what time it was actually formed
I could not make out, as, from its extreme transparency
and similarity of colour to the rest of the animal, it was
very difficult of detection. The cilia could be seen
vibrating within the shell for some time after the ani-
mal became quiescent a few isolated cilia at one of the


extremities, not observed before, being the only ones
that remained to perform their functions externally.
These produced a partial current without propelling the
animal through the water, as at this stage it gave up its
natatory habits and took to a quiet life. The internal
portion, the parts of which could not be very distinctly
made out, appeared to be undergoing a process of deve-
lopment. The mass was continually changing its form,
the separate parts being extended alternately in different
directions, and a portion, probably the incipient foot,
was occasionally pushed beyond the margin of the shell.
At this point of development further observations were
unfortunately arrested by the death of the whole colony
in consequence of the water becoming impure, and my
situation at a distance from the sea preventing my get-
ting an immediate fresh supply. The whole period that
I had kept them was not above five or six days ; so that
their development had been pretty rapid. After the
death of the animals the shells remained at the bottom
of the glass. They were of an elliptical form, straight
at the upper margin, where they were attached, though
the hinge did not appear to be yet formed ; the whole,
excepting in the elongated form, had very little resem-
blance to the adult shell. "

I am sure my readers will not regret my having
reproduced such a faithful and striking picture by one of
our great masters of British zoology. It agrees on the
whole with the account furnished by Loven, and espe-
cially with his observations as to the development of
the embryo of Modiolaria marmorata and Lascea rubra.
The metamorphosis in Modiolaria is stated to have
commenced about the third day after the spawn was
deposited, being the same period as that which Alder
noticed in Montacuta ferruginosa. The shell is apt to


become coated with a thick but irregular layer of hard
ochreous dirt, like iron-rust. I suspect that this in-
crustation is caused by a continual deposit and accumu-
lation of faecal matter from the animal, which is not
carried off in consequence of its sedentary habits and of
the water in which it lives being free from currents.
The same remark applies to species of Pisidium and
other freshwater shells, as well as to many of the ma-
rine bivalves. Forbes and Hanley observe that M.fer-
ruginosa is " a scarce shell." This of course is only
in comparison with other species; but the common
notion of rarity is not quite correct. I consider that
" local" would be a more appropriate word than "scarce"
with regard to the occurrence of marine testacea. The
difficulty of procuring some particular kinds may en-
hance their value to collectors ; but probably all kinds
are prolific, and differ in that respect from many of the
larger land mammals. There certainly cannot exist a
" unique " specimen of any shell in nature. In the
present case single valves may be found in tolerable
plenty on several of our sandy beaches, and perfect spe-
cimens may be got by dredging in the sheltered lochs of
the west of Scotland and in rather deep water off our
southern coasts. The beaks are often fissured or notched
from their being squeezed close together by the strong
and elastic cartilage, the shell being too fragile to resist
such pressure.

The proportions of length and breadth vary greatly
in specimens, which may account for the diversity of
names which this species has from time to time re-
ceived. As I have already incidentally noticed, it ap-
pears to be the Amphidesma purpurascens of Lamarck ;
Brown called it Tellimya elliptica and T. glabra,
S. Wood T. ovata, Leach Amphidesma Goodalliana,


Recluz Erycina Franciscana, and Loven Montacuta

Among some small shells sent to me by Mr. Robert
Dawson, and collected by him on the Aberdeenshire
coast, is a minute single valve, which I cannot identify
with any known species, whether recent or fossil. Its
shape is obliquely triangular, with rounded margins ; it
is compressed, rather solid, glossy, and smooth or marked
only by the lines of growth ; the beaks are blunt and
not prominent; the hinge-line is small and straight;
the teeth somewhat resemble those in the right valve of
Montacuta bidentata, but they are much shorter and
nearly on a level with the hinge-line, the tooth on the
broader side being considerably larger and stronger than
the other ; the inside is nacreous, with a plain margin.
The shell appears to be full-grown ; but its size is barely
one-fifteenth of an inch in length, and rather less in
breadth. If more specimens are found, I would propose
for this species the name of Dawsoni, as a fit compli-
ment to its discoverer, a zealous and intelligent con-

When dredging at Falmouth in 1839 I obtained a
recent single valve of the species, which Searles Wood
described and figured in his Monograph of the Crag
Mollusca (Palseont. Soc. Trans. 1850, p. 131, tab. xi.
f. 3 a-c) as Montacuta donacina, from the Coralline
Crag at Sutton. I am, no less than Mr. Wood, quite
unable to say in what genus this curious shell should be
placed. My specimen is a right valve, and it has a
minute tubercular tooth on the longer side of a small
cartilage-pit. In shape it is a miniature Zenatia (a
genus founded by Dr. Gray), but having an external

LAS^A. 217

Genus III. LASSES' A*, Leach. PI. V. f. 2.

BODY oval : mantle folded on the anterior side (being the
longer and larger end of the shell), so as to form a wide, but
incomplete, incurrent tube : the excurrent tube is very short and
inconspicuous, placed on the opposite side : foot long, tongue-
shaped, protruolmg when in motion through a slit in the ex-
current tube at its base.

SHELL roundish-oval: beaks straight: cartilage long and
cylindrical, divided or split lengthwise, and clasping the
hinge-plate, in each valve, on the smaller and narrower side
of the shell, being the posterior end : hinge containing in the
left valve a minute thorn-like cardinal tooth, and in each
valve two remarkably strong lateral teeth.

The late Captain Brown proposed this genus in 1827,
on the authority of Dr. Leach, for the Cardium rubrum
of Montagu ; and although he says nothing about the
animal, and not much more about the shell, I think the
genus is a good one, and I therefore adopt the name
above given to it. M. Recluz, apparently unaware of
his having been anticipated, gave in 1843 another name
(Poronia) to the same genus; but his description is
positively incorrect. He says of the animal, that it has
on the posterior side two lobes, and two tubes which are
disunited ; and of the shell, that the hinge has two cardi-
nal teeth in each valve, besides lateral teeth, and that
the cartilage is placed in an oblique groove. It will be
seen that my description of the generic characters is
very different from that of M. Recluz ; and were it not
for the certainty that we both mean not only the same
genus, but also the same species, I could not believe
that our respective descriptions had been drawn from
the same object. The present genus is intermediate
between Montacuta and Kellia, and partakes of the

* A meaningless name ; possibly a corrupt derivation from \aivi jiov, a
little shield.



leading characteristics of each. With the former it
agrees in having the cartilage placed at the shorter end
of the shell, a position contrary to that in Kellia, and
with the latter in the mantle being folded on the ante-
rior side, though not so completely as in that genus.
The position of the cartilage or ligament is by no means
unimportant, because it indicates the posterior side ; and
the empty shell thus serves to determine the place, and
often the nature, of the organs which had composed the
frame of its late occupant.

It is very probable that the shell which Adanson
called " Le Poron " belongs to this genus ; but his
notice of it is unusually brief and obscure. He says that
it has two small triangular teeth in each valve, which
form the hinge, that it is at most only two lines in dia-
meter, and that it is whitish and sometimes of a violet
colour, chiefly towards the hinge. He evidently did not
know the animal, for he included the Poron among the
species of his genus Chama, which he described as having
three openings in the mantle, two of which take the form
of a rather long tube. It would be a waste of etymolo-
gical research were we to endeavour to trace the derivation
of the word " Poron." Adanson tells us, in the preface
to his most admirable work on the Mollusca of Senegal,
that he preferred inventing such chance names as had
the least meaning, and had no relation to other names
or known objects. Perhaps Dr. Leach had the same
idea in selecting some of his generic names. However
that may be, in his posthumous work on the Mollusca
of Great Britain he seems to have changed Lasaea for
the more classically correct name of Autonoe, placing it
in the family Venerida, although calling the species (after
describing it) " Lasea rubra."

The Lasaa are of a minute size, and usually inhabit

LAS^A. 219

the littoral zone, where they congregate in vast num-
bers, at the roots of small seaweeds, as well as in the
crevices of rocks and in the empty shells of Balani. On
some coasts they live as much out of the sea as in it,
a sufficient supply of water being retained within the
close-fitting valves to keep the gills moist until the
return of the tide ; and in many cases they must fast for
a long time, because they are found in places which are
covered by the sea at high springs only. A little fresh-
water bivalve (Pisidium pusillum) is also occasionally
amphibious. We have but one species of Lasaa, and
that is viviparous. Other species, however, have been
noticed in various parts of the world :

" ..... Pr'ythee, think
There 's livers out of Britain."

1. LAS^A RU'BRA*, Montagu.^ ^. 3?

Cardium rubrum, Mont. Test. Brit. p. 83, tab. 27. f. 4. Kellia rubra,
F. & H. ii. p. 94, pi. xxxvi. f. 5-7 (as Poronia rubra), and (animal)
pi. O. f. 3.

BODY white : mantle having its margin apparently plain and
without tentacles : eoccurrent tube sessile and concealed within
the mantle : foot broad at the base, the extremity being rather
rounded than pointed ; its bluish-white and transparent hue
is variegated by a line of dull but intense flake-white, which
runs from one end to the other.

SHELL oval, with often a circular or triangular and rather
oblique outline, ventricose, not very thin or glossy : sculpture,
distant lines of growth and close-set wavy concentric striae,
besides more numerous but much finer longitudinal stria3,
which are so excessively minute as only to be seen with a
powerful lens : colour milk-white, tinged more or less deeply
with purplish-red, especially towards the hinge : epidermis
yellowish, rather thick : margins somewhat truncate and
rounded at the smaller or posterior end, slightly curved in
front, with sometimes a byssal sinus or indentation in the

* Red.



middle, produced or wedge-like and rounded at the anterior
end : beaks broad, blunt, prominent, and contiguous ; they are
placed about two -fifths nearer to the posterior end : hinge-line
curved, occupying rather more than one-fourth of the circum-
ference : cartilage large, yellowish-horncolour, attached to the
shell below the hinge-plate and lodged on an oblique shelf :
Tiinge-plate very broad, thick, and strong : teeth, in the right
valve two triangular laterals with sharp points, the anterior of
which is a little more raised than the other ; in the left valve
similar laterals, besides a minute cardinal and erect tooth
directly below the beak ; the laterals in each valve lock into
corresponding grooves in the other : inside partially nacreous,
but otherwise of a dull hue ; margin plain : pallial scar scarcely
visible, but evidently existing on account of the adhesion of
the mantle inside the front margin : muscular scars oval and
distinct. L. 0-85. B. 0-1.

Var. pallida. Shell yellowish-white and nearly trans-
parent, without any tinge of purple or red.

HABITAT : Everywhere in crevices of rocks, inside the
empty cups of Balani and among the tufts of Lichina
pygmaa, near high-water mark, and at the roots or
footstalks of Corallina officinalis and other seaweeds,
and on mussel-beds, between tide-marks ; sometimes it
is found at depths varying from 3 to 20 fathoms. The
variety is not uncommon. This species is a Coralline
Crag shell. Steenstrup has found it in Iceland, and
Lilljeborg at Grip in Upper Norway ; but I am not
aware of any other northern locality. It is widely
diffused southwards from the north of France to the
Canary Isles, and throughout the Mediterranean. Spe-
cimens for which I am indebted to the kindness of
Mr. Cuming (so renowned for his unrivalled collection
of shells, as well as for the extent of his coiichological
experience), and taken by him on the south-western coast
of America, cannot be distinguished from the European
species ; and Dr. Philip Carpenter is of opinion that a
species from the Gulf of California is the same as ours.

LASJ2A. 221

L. rubra has been recorded by Sars among arctic shells
occurring in newer tertiary strata in the diocese of

Dr. Turton was the first who noticed the curious fact
that this minute mollusk is viviparous. It does not
appear to be prolific, as seldom more than twenty young
ones are to be seen at any one time in the shell of the
parent. They are fully formed while in this stage of
growth, and their shells have even a tinge of purplish-
red on each side of the beaks. Mr. Clark says the
ovary contained no young in specimens which he pro-
cured in the winter. The same may perhaps be said of
most mollusca, whether viviparous or oviparous, as well
as of other animals the season of whose loves in a state
of nature does not commence until

" species patefactast verna diei,

Et reserata viget genitabilis aura favoni."

A discussion took place some years ago, between
Mr. Clark on the one side, and Messrs. Alder and Han-
cock on the other, as to the use of the anterior tube in
this species and in Kellia suborbicularis, both of which are
viviparous. Mr. Clark contended that it was an organ
of reproduction, in consequence of his having observed
the fry ejected through it. His opponents disputed this
uterine function, and showed that the tube serves to
convey water to the gills. My own observations induce

Online LibraryJohn Gwyn JeffreysBritish conchology; or, An account of the Mollusca which now inhabit the British Isles and the surrounding seas (Volume 2) → online text (page 18 of 39)