■»•; 



MOLLUSCA. 



[Conch acea. 



The want of crenulations on the margin of this shell, will at 

 once distinguish it from the C. Danmoniensis. 



Found on the coast of Caithness, and the Frith of Forth, 

 Scotland ; and the Downshire coast, Ireland. 



3. Crassina elliptica, pi. XXXVIII, f. 3. 

 Crassina elliptica, First Ed., pi. 18, f. 3. 



Shell thick, nearly oval, rather compressed; umbones pointed, 

 considerably turned towards the anterior side ; beneath which 

 is a cordiform, deep lunule ; cartilage side rather straight ; with 

 many regular, transverse, nearly straight, obsoletely striate ribs; 

 external surface of a dark yellowish-brown ; inside white, 

 smooth ; margin plain, rather thickened, with a slight rim at 

 the edge. 



Found in the Friths of Forth and Clyde. 



The more thickened margin, and elliptical form of this shell, 

 will at once distinguish it from its congeners. 



4. Crassina ovata, pi. XXXVIII, f. 11, 12. 

 Crassina ovata, Brown, Edin. Joum. Nat. and Geo. Science, 



I, p. 12, pi. 1, f. 8 ; Crassina Gairensis, Nicol, MSS. 



Shell thick, strong, subcompressed ; umbones small, pointed, 

 with a lanceolate, deep, and large lunule below them ; surface 

 of a deep burnt umber-brown, with numerous, broad, elevated, 

 concentric, transverse ridges, which become nearly obsolete 

 as they approach the base of the valves ; inside bluish-white, 

 with a broad and plain margin ; muscular impressions large 

 and deep. 



This species has much the appearance of C. Scotica, but 

 differs from it in being more ovate, much stronger, the mus- 

 cular impressions being nearly double the size, and in the lunule 

 being larger and deeper. 



Inhabits the Gair Loch, in the river Clyde, where it is rather 

 |)lentiful. 



5. Crassina sulcata, pi. XXXVIII, f. 10. 



Crassina sulcata, First Ed., pi. 18, f. 10; Venus sulcata, Mon- 

 tagu, p. 131 ; Lamarck, V, p. 592 ; Maton and Rackett, p. 81, 

 pi. 2, f. 2; Brown, Werneriam Mem., II, p. 510; Astarte sul- 

 cata, Fleming, p. 439- 



Shell strong, thick, suborbicular, subangular, and considerably 

 compressed ; umbones very prominent, nearly central, acute, 

 and but slightly turned to one side, with a lanceolate, shallow 

 lunule; external surface of a yellow-chestnut, strong epidermis, 

 and a series of very broad and flat transverse ridges, which 

 become nearly obsolete at the sides, and towards the umbones ; 

 cartilage side somewhat flattened; basal margin well rounded; 

 inside smooth, white, and very glossy from the pallial impression 

 to the margin, which is very finely crenatcd at the edge; hinge 

 teeth very strong. Length about seven-eighths of an inch ; 

 breadth not quite so much. 



This shell is very distinct from its congeners; the transverse 

 ridges are greatly broader, and very much depressed; the space 

 between the pallial impression much broader and flatter, and 

 the epidermis more clear. 



Turton has completely mistaken this very distinct species, in 

 quoting Montagu. His description and figures apply to C. Dan- 

 moniensis, from which the present is totally distinct. 



Found in Orkney and Cornwall; and has been dredged alive 

 at Bray, Ireland. I met with odd valves in the Frith of Forth, 

 and on the beach at Montrose. 



6. Crassina compressa, pi. XXXVIII, f. 4, 5. 



Crassina compressa, First Ed., pi. 18, f. 4, 5; Montagu, Sup., 

 p. 43, pi. 26, f. 1, 1, 1. 



Shell strong, thick, nearly orbicular, compressed ; umbones 

 prominent, turned slightly to the anterior side, beneath which 

 is a cordiform lunule ; surface with a few irregular, remote, 

 concentric wrinkles, which become obsolete towards the base 

 of the valves ; of a dark umber-brown colour, beneath which 

 the shell is covered with transverse, irregulai, almost obsolete 

 striae ; inside smooth, white ; margins broad, flat, and thin, and 

 destitute of crenulations. 



This species differs from any of the preceding, in being des- 

 titute of distinct ridges, and is more orbicular. The young are 

 of a pale yellowish-brown, and are almost smooth, but when the 

 epidermis is removed, they betray a finely striated surface. I 

 obtained some live specimens, by dredging, off the coast of 

 Dunbar. The only full grown specimen which I have seen, is 

 that from which Montagu's shell was described and drawn, as 

 well as my figure, and is in the cabinet of my late friend David 

 Falconer, Esq., of Carlowrie. 



7. Crassina corrugata, pi. XL, f. 24. 

 Crassina corrugata, First Ed., pi. 16, f. 24. 



Shell strong, somewhat triangular, compressed ; umbones 

 small, obtuse, and very slightly reflexed; beneath them a large, 

 deep, lanceolate lunule ; surface covered with a reddish-brown 

 epidermis, transversely wrinkled, and with nearly obsolete, 

 transverse, numerous, irregular stria?; inside smooth, bluish- 

 white ; margin smooth, and entire, sloping gradually towards 

 the centre, but not deep; teeth very strong. Length an inch 

 and a half; breadth nearly two inches. 



This shell differs from the other species, in the posterior 

 margin being somewhat produced, and in its total destitution of 

 ribs ; and is much flatter, in proportion to its size. 



Discovered at Greenock, by my friend Stewart Ker, Esq. 



8. Crassina depressa, pi. XXXVIII, f. 2. 

 Crassina depressa, First Ed., pi. 18, f. 2. 



Shell compressed, transversely and obliquely subovate ; um- 

 bones rather prominent, and slightly reflexed, with a lanceolate, 

 deep lunule under them ; colour of a dark reddish-brown, with 

 many flattened, transverse ridges, and narrow, shallow, inter- 

 vening furrows; inside white, smooth; margins plain, and rather 

 thickened in the edge. Length nine-eighths of an inch; breadth 

 nearly eleven-eighths. 



This differs from the C. Scotica, in being more transversely 

 elongated, oblique, more compressed, with the basal line more 

 parallel, the transverse ridges more numerous, very flat, and 

 almost obsolete. 



Found in the Frith of Forth ; but I have hitherto only met 

 with dead and detached valves. 



9. Crassina striata, pi. XXXVIII, f. 6, 7, 8. 

 Crassina striata, First Ed., pi. 18, f. 6, 7, 8. 



Shell suborbicular, very strong, and rather ventricose ; um- 

 bones produced, and rather blunted at the beaks, placed nearly 

 central, and slightly reclining ; beneath them a deep, lanceolate 

 lunule; surface with numerous, regular, fine, transverse striae, 

 covered with a dark olive-brown epidermis ; inside white, 

 smooth, and glossy ; cartilage impressions very deep. Length 

 three-eighths of an inch ; breadth half an inch. 



