Pectinides.] 



MOLLUSCA. 



71 



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. 19, pi. XXIII, is from the Frith of Forth; it is a lusus, 

 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. 19, pi. 71, f. 660; 

 Turton, Biv., p. 205, pi. 17, 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 flat, 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, pi. 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 stria? ; entire 

 surface invested with fine, concentric, undulating stria?, 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 Jacobceus, 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 striae ; 

 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 stria?, 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 

 es unequal. 



in si~e ; auri- 



3. Pecten operculars, pi. XXIV, f. 1. 

 Pecten opercidaris, First Ed., pi. 33, f. 1 ; Linne, Syst., p. 

 1147; Lamarck, VI, p. 172; Montagu, p. 145; Turton, Biv., 



