CONCHACEA.] 



MOLLUSCA. 



99 



5. Lucina LEUCOMA, pi. XXXIX, f. 29. 



Lucina leucoma, Turton, Biv., p. 113, pi. 7, f . 8 ; Loripea 

 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 striae, 

 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 (he 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 flexuosa, First Ed., pi. 17, f. 4, 5, 6, 7 ; Fleming, p. 

 442; Cryptodon flexuosus, Turton, Biv., p. 121, pi. 7, f. 9, 10; 

 Tellina flexuosa, Montagu, p. 72 ; Brown, Wernerian Mem., 

 II, p. 508; Venus simiosa, Donovan, II, pi. 42, f. 2; Bequania 

 flexuosa, 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 by a broad, 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. 



Arcopagia crassa, First Ed., pi. 16, f. 8 ; Leach, MSS., p. 9 ; 

 Tellina ci-assa, 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, pi. 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 off 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 the 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 striae, 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 



