MOLLUSCA. 
71 
Pectinides.] 
1. OsTREA EDULis, pi. XXIII, f. 19> and pi. XXX,* f. 
6, 7. 
Ostrea edulis, First Ed., pi. 31, f. 19; Linne, Syst., p. 1148; 
Lamarck, VI, p. 205; Pennant, p. 102, pi. 62, f. 70; Da Costa, 
p. 154, pi. 11, f. 6 ; Montagu, p. 151. 
Shell suborbicular, rugged, foliaceous, the folds lying over 
each other in irregular order ; the points of the umbones apart 
from each other ; lower valve largest, and more concave than 
the upper one ; valves closed all round ; the external foliations 
frequently in the form of divergent, longitudinal, irregular, 
interrupted ribs, and sometimes irregularly and transversely 
striate ; margins of the valves slightly undulated ; outer surface 
of a dull brown colour ; inside white. 
This shell is liable to great variety, both in size and form ; 
those found at Carrickfergus, in Ireland, are very large and 
ponderous, generally measuring seven inches and upwards in 
diameter ; while at Carlingford and Milford they are very small. 
They inhabit many of the coasts around Britain and Ireland. 
Fig. 19j ph XXIII, is from the Frith of Forth; it is a Ittsus, 
with a singular prolongation of the hinge. 
Fig. 6, 7, pi. XXX,* is from Milford, and is the ordinary size 
of that locality ; this variety is provided with a row of teeth- 
like processes, diverging on each side of the umbo, which is 
rather acute and triangular. 
2. Ostrea parasitica, pi. XXIII, f. 20, 21. 
Ostrea parasitica, Chemnitz, VIII, p. 19j ph 71> f. 660; 
Turton, Biv., p. 205, ph 17j f. 6, 7; Fleming, p. 392. 
Shell small, thin, longitudinal, seldom exceeding two inches ; 
of a drab or greenish-brown colour ; sometimes with radiations 
of black or brown ; beaks generally incurved ; surface usually 
smooth ; inside white, with slight pearlaceous reflections. 
This species is invariably attached to other bodies, and sub- 
ject to great variety in form, depending upon the substance to 
which it is fixed. It is met with on some coasts adhering to 
stones, rotten wood, &c., near low water-mark. I found several 
specimens attached to a piece of rotten wood, at Hull. I do 
not believe that all the young of the O. edulis are parasitical, 
as some authors imagine. 
Family III. — Pectinides. 
Shell generally regular, and not foliaceous ; ligament placed 
interiorly, or partly so. 
Genus 5. — Pecten Bruguiere. 
Shell inequilateral ; the under valve generally more convex 
than the upper one ; subequilateral, with many grooves or ribs, 
radiating from the umbones to the margins ; provided with two 
auricles, which are, for the most part, irregular in size, close 
below one of them in the upper valve is a small notch for the 
passage of the lyssus ; muscular impression large, placed some- 
what to one side ; palliel impression destitute of a sinus ; hinge 
linear, without teeth ; ligament consisting of three portions, of 
which the two lateral parts are elongated, and follow the hinge 
line, the third portion thick and triangular, and fitted into a tri- 
angular shallow pit within the hinge. 
Section I. — One valve jiat, the other deep and convex. 
1. Pecten maximus, pi. XXV, f. 1. 
Pecten maximus, First Ed., pi. 32, f. 1 ; Lamarck, VI, p. 
163; Montagu, p. 143; Fleming, p. 383; Turton, Biv., p. 207; 
Forbes, p. 39 ; Ostrea maxima. Pennant, IV, p. 99? ph 59> f* 
61; Donovan, pi. 49; Brown, Wernerian Mem., II, p. 513; lb., 
Ency. Brit., p. 417. 
Shell suborbicular; upper valve convex; the under flat, 
shorter than the other one, and depressed near the umbo, in 
which situation the ribs are nearly obsolete, and devoid of 
striae; each valve provided with fourteen or fifteen rounded, 
gently undulating, divergent ribs, with obsolete ones on both 
sides ; the whole of which, together with the interstices, are 
covered with very strong, irregular, divergent striae ; entire 
surface invested with fine, concentric, undulating striae, and 
inequidistant, remote lines of growth ; provided with two nearly 
equal, rectangular auricles, covered with narrow, rather close, 
rounded, diagonal ribs, these are crossed by numerous, thick- 
set, undulating, longitudinal striae, and inequidistant lines of 
growth; whole surface of a reddish-brown colour; inside white, 
with flattened, broad ribs, and a rufous-brown, very broad, ill 
defined fillet round the margin, which is very slightly scalloped. 
Length five inches ; breadth six inches. 
Found in deep water on many of the British coasts, namely, 
Dorsetshire, Devonshire, and Northumberland; Dublin Bay, 
Portmarnock, Lough Strangford, and Bray, Ireland. 
2. Pecten Jacob^us, pi. XXIV, f. 5. 
Pecten Jacohceus, First Ed., pi. 33, f. 5 ; Lamarck, VI, p. 
163; Turton, p. 207; Pennant, IV, p. 100, pi. 60, f. 62; 
Fleming, p. 383; Montagu, p. 144; Ostrea Jacobcea, Donovan, 
pi. 137 ; Brown, Ency. Brit., p. 417. 
Shell with seventeen or eighteen very convex, divergent 
ribs ; the upper valve flat, rufous, with rounded ribs, and a 
smooth whitish depression near the umbo, in which situation 
the ribs are nearly obsolete; under valve very convex, pure 
white, pale brown, or flesh-coloured; ribs angulated, rising 
abruptly at the sides, and gently rounded on the surface, the 
interstices with strong, inequidistant, longitudinal furrows, 
usually three to each rib, the central one being considerably 
broader than the others, and crossed by fine transverse striiB ; 
auricles equal, rectangular, with nearly obsolete, diagonal ribs, 
two or three of which are stronger towards the hinge line, 
or top of the auricles, these are crossed by extremely fine, 
somewhat irregular, waved striae, and striated; inside white, 
slightly tinged with a reddish hue near the margin, which is 
scalloped. Length three inches; breadth four inches; but is 
found much larger in the Bay of Naples, and other continental 
localities. 
Dredged in deep water off Poole and Weymouth, Dorset- 
shire ; Cornwall ; and at Scarborough, Yorkshire. It is, how- 
ever, a very rare British species. 
Section II. — Both valves convex, and equal in size; auri- 
cles unequal. 
3. Pecten opercularis, pi. XXIV, f. 1. 
Pecten opercularis. First Ed., pi. 33, f. 1 ; Linne, Syst., p. 
1147; Lamarck, VI, p. 172; Montagu, p. 145; Turton, Biv., 
