MOLLUSCA. 
99 
CONCHACEA.] 
5. Lucina leucoma, pi. XXXIX, f. 29> 
Lucina leucoma, Turton, Biv., p. 113, pi. 7, f . 8 ; Loripes 
leucoma, Fleming, p. 430. 
Shell somewhat oblique, orbicular, slightly produced and 
angular on the anterior side, and generally a little flexous 
under the beaks and on the opposite side; umbones pro- 
minent, with a curvature under them ; exterior surface of a 
chalky-white, with regular, crowded, transverse, raised strise, 
and deeper wrinkles ; crossed by extremely fine, close-set, lon- 
gitudinal lines. 
Turton, on whose authority we give this shell, says he has 
remarked in some specimens a small remote tubercle on each 
side of the hinge, resembling obscure lateral teeth. 
Inhabits Torbay, the British Channel, and Guernsey. 
Genus 22 — Cryptodon — Turton. 
Shell transversely subglobose, equivalve, nearly equilateral, 
closed ; umbones unequal, nearly central, beneath them a large, 
deep, elongated, cordiform lunule ; hinge of the right valve 
with a single, irregularly-formed, erect, triangular tooth, which 
fits externally into a small cavity below the umbones in the 
opposite valve, and a narrow lateral cavity, for the reception 
of a triangular, flat, hollow, lateral tooth of the other valve, 
which is provided also with an ill-defined, nearly flat, primary 
tooth ; both valves with a large, double, muscular impression 
on one side, and small single ones on the other side ; pallial 
impression destitute of a sinus, and situate low in the valves ; 
ligament internal, a small portion only being visible through 
the seam ; an elongated, pointed lunule, hollow at the side 
and elevated in the centre, invests the entire length of the 
cartilage slope. 
1. Cryptodon flexuosus, pi. XXXIX, f. 4, 5. 
Lucina jlexuosa. First Ed., pi. 17, f. 4, 5, 6, 7 ; Fleming, p. 
442; Cryptodon jiexuosus, Turton, Biv., p. 121, pi. 7, f- 9, 10; 
Tellina jlexuosa, Montagu, p. 72 ; Brown, Wernerian Mem., 
II, p. 508 ; Venus sinuosa, Donovan, II, pi. 42, f. 2 ; Bequania 
fiexuosa, Leach, MSS., p. 9- 
Shell subtriangular, subglobose, thin, pellucid, fragile, white ; 
umbones small, slightly inflected, and unequal, that of the right 
valve smallest, the other resting on the cavity above the pri- 
mary tooth of the opposite valve; beneath them a large cordate 
lunule, with an elongated lunule on the cartilage side, pointed 
at both ends ; a sulcus emanates from the umbones in both 
valves, running nearly parallel with the cartilage, terminating at 
one side, where it forms a pretty large sinus, or flexure, at the 
edge ; whole surface moderately glossy, remotely and rather 
irregularly striated concentrically ; hinge with a single, erect, 
triangular tooth in one valve, and a flat, nearly obsolete one in 
the other ; inside smooth, glossy, white, exhibiting slightly 
nacred reflections, and some indications of longitudinal radii ; 
margins plain, and very acute. 
. Figs. 6 and 7 is a variety of this shell, figured by Donovan, 
which differs from any specimens we have seen. 
This interesting little shell is met with, although very spa- 
ringly, on most of the British and Irish coasts. 
Genus 23 — Arcopagia — Leach. 
Transverse, equivalve, inequilateral; right valve subdepres- 
sed ; umbones very small, nearly straight ; with two primary 
teeth in both valves, each of the larger ones cleft ; left valve 
with two remote, lateral teeth, that on the anterior side large, 
with a sinus betwixt it and the margin, for the reception of 
the lateral tooth of the opposite valve; muscular impressions 
large; pallial impression interrupted hy a hroad, tongue-shaped, 
oblique, perpendicular, nearly central sinus, defined by a deep, 
irregular groove ; margin very broad, and very glossy, as far as 
the pallial impression ; ligament subexternal. 
1. Arcopagia crassa, pi. XL, f. 8. 
Arcoqmgia crassa. First Ed., pi. 16, f. 8; Leach, MSS., p. 9; 
Tellina crassa. Pennant, IV, p. 87, pi. 48, f. 28 ; Montagu, p. 
65; Brown, Wernerian Mem., II, p. 508; Fleming, p. 436; 
Forbes, p. 46; Turton, Biv., p. 109, ph 7, f» 2; Tellina rigida, 
Donovan, III, pi. 103. 
Shell strong, thick, somewhat oblique, transversely subovate, 
a little subtruncated on the extremity of the cartilage side, and 
slightly inequivalve, the left one being the larger, and consider- 
ably more convex than the other, which is much more com- 
pressed ; umbones small, beaks short, and rather obtuse, placed 
considerably OS’ the centre towards the cartilage side, and point- 
ing to the opposite side ; beneath them a rather narrow, deep, 
elongated, lanceolate lunule; colour white, cream-white, or pale 
sulphur-yellow, rarely skin-coloured or pale sulphur-yellow ; 
sometimes plain, but more frequently beautifully radiated, with 
broad and narrow, variously disposed, rays of pale red, flesh- 
colour, or reddish-purple, which are always more distinctly 
defined towards their bases ; whole surface covered with nume- 
rous, strong, pretty regular, concentric striae, becoming wider as 
they approach the base, these are crossed by numerous, indis- 
tinct, shallow, longitudinal striae, which can only be seen by the 
aid of a strong lens, and are most perceptible in tbe interstices 
between the transverse striae, and interrupted at intervals by a 
few distinct lines of growth ; a rather broad sinus extends from 
the umbones towards the base, on the posterior side of the right 
valve, with a corresponding ridge on the opposite valve ; inside 
very glossy, bluish-white, rich golden-yellow, or in some of a 
beautiful rose-colour, or deep red ; sometimes streaked and 
blotched in a very handsome manner ; hinge with two cardinal 
teeth in each valve, one of which is cleft, and two strong, elon- 
gated, lateral teeth in both valves; a little way below the pallial 
sinus are, generally, a few irregularly disposed, shallow punc- 
tures ; margins plain, with a slight groove on the edge of the 
left valve, for the reception of the edge of the other valve. 
This interesting species is an inhabitant of most of the British 
and Irish coasts. 
2. Arcopagia ovata, pi. XL, f. 9, 10. 
Arcopagia ovata. First Ed., pi. 16, f. 9, 10. 
Shell strong, thick, transversely ovate, suboblique, one valve 
convex, and somewhat larger than the other, which is compres- 
sed ; umbones placed nearer one side, small, and rather blunt ; 
of a pale straw-colour; covered with strong, concentric, rather 
regular strise, which feel rough to the touch, with inequidistant 
lines of growth ; destitute of a lateral sinus, or ridge ; sides 
more uniformly rounded than in the foregoing species, and 
without the slight truncation ; hinge with a large bifid, and a 
