96 MOLLUSCA. 
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, pl. XXXVIII, f. 3. 
Crassina elliptica, First Ed., pl. 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, pl. XXXVIII, f. 11, 12. 
Crassina ovata, Brown, Edin. Journ. Nat. and Geo. Science, 
I, p. 12, pl. 1, £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 
plentiful. 
5. Crassina sutcara, pl. XXXVIII, f. 10. 
Crassina sulcata, First Ed., pl. 18, f. 10; Venus sulcata, Mon- 
tagu, p. 131; Lamarck, V, p. 592; Maton and Rackett, p. 81, 
pl. 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 crenated 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. 
[Concnacrka. 
6. Crassina compressa, pl. XXXVIII, f. 4, 5. 
Crassina compressa, First Ed., pl. 18, f. 4,5; Montagu, Sup, 
p- 43, pl. 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, irregular, almost obsolete 
strie ; 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 haye 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, pl. XL, f. 24. 
Crassina corrugata, First Ed., pl. 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 striae; 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. CRassINaA DEPREsSA, pl. XXXVIII, f. 2. 
Crassina depressa, First Ed., pl. 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 eleyen-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 srriaTa, pl. XXXVIII, f. 6, 7, 8. 
Crassina striata, First Ed., pl. 18, f. 6, 7, 8. 
Shell suborbicular, very strong, and rather yentricose ; 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 striz, 
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. 
