110 



MOLLUSCA. 



[MVABIA. 



anterior side truncated, with a shallow, oblique furrow running 

 near to the hinge line, most deeply defined in the convex 

 valve ; basal line nearly parallel ; surface of a sand-colour, 

 strongly wrinkled, and slightly and irregularly striated concen- 

 trically ; when viewed through a lens presenting the appear- 

 ance of shagreen, and feels very rough to the touch; behind 

 the cartilage side one valve turns upwards, and embraces the 

 edges of that opposite ; hinge with one broad, very strong, 

 thickened, complicated, bipartite, horizontal, tooth-like plate 

 in each valve, to which the cartilage is attached, that of the 

 convex valve sunk below the level of the hinge line, and in 

 the flat valve almost entirely exposed above it ; inside white, 

 and glossy. 



Found on the Devonshire coast of a large size, but is a very 

 local species. 



2. Thracia convexa, pi. XLIV, f. 3. 



Anatina convexa, First Ed., pi. 11, f. 3; Turton, Biv., p. 

 44, pi. 4, f. 1,2; Mya convexa, Wood, Gen. Conch., p. 92, pi. 

 18, f . 1 ; Brown, Ency. Brit., 6th Ed., VI, p. 404; Thracia 

 convexa, Leach, MSS., p. 5; Amphidesma convexum, Fleming, 

 p. 431. 



Shell subtriangular, very convex, and extremely brittle ; um- 

 bones obtuse, placed nearly central, a little inflected, and almost 

 touching each other; sides rapidly descending, the posterior one 

 rounded, anterior one truncated ; the truncation bounded by 

 an elevated ridge, which takes its rise from the beaks, and ter- 

 minates on the basal margin, which is a little arcuated; surface 

 of a sand-colour, concentrically wrinkled, obsoletely and irregu- 

 larly striated, and very indistinctly granulated ; dentary plate 

 obliquely elevated, narrow, with several longitudinal furrows for 

 the reception of the cartilage ; inside smooth, white, or pale 

 reddish-brown. 



In the adult shell the umbones are so very contiguous, that 

 they only permit the valves to open to a small extent, not 

 more than half an inch. 



Found on the Devonshire and Welsh coasts, and also in 

 Ireland ; and odd valves are frequently met with at Cramond 

 Island, Frith of Forth ; Turton mentions Paington Sands. It 

 is an extremely local species. 



3. Thracia pubescens, pi. XLIV, f. 6. 



Anatina villosiuscula, First Ed., pi. 11, f . 6 ; Macgillivray, 

 Phil. Journ., 1827, pi- 1, f- 10, 11 ; Anatina declives, Turton, 

 Biv., p. 47; Mya declivis, Montagu, pi. 1, f. 2; Amphidesma 

 declive, Fleming, p. 432. 



Shell transversely oblong-ovate, compressed, thin ; umbones 

 placed to one side; posterior side much rounded; anterior side 

 contracted, and truncated; an elevated ridge emanates from 

 below the umbones, and terminates at the base of the trunca- 

 tion ; one central, flat, transverse tooth in each valve ; external 

 surface with a fine pubescent appearance, when viewed through 

 a strong lens. 



Found in Dublin Bay, the Dorsetshire coast, and Frith of 

 Forth. 



4. Thracia ovata, pi. XLIV, f. 1. 

 Anatina ovalis, First Ed., pi. 1 1, f. 4. 



Shell transversely ovate, subtriangular ; umbones nearly cen- 

 tral, very obtuse, and not inflected; sides almost equally round, 

 but very slightly truncated on the anterior one ; hinge with a 

 narrow, transverse tooth ; surface a little shagreencd, which, 



however, can only be seen by the aid of a strong lens; colour 

 pale yellowish-white ; inside white. 



I found this shell at Color Cots sands, Northumberland. It 

 may be merely an accidental variety of T. declivis. 



5. Thracia distorta, pi. XLIV, f. 7. 



Anatina distorta, First Ed., pi. 11, f. 7; Turton, Biv., p. 48, 

 pi. 4, f. 5 ; Mi/a distorta, Montagu, p. 42, pi. 1, f. 1 ; Amphi- 

 desma distortum, Fleming, p. 432. 



Shell rather convex, transversely subovate, thin, fragile, 

 rugose, and distorted, particularly towards the base of the 

 valves ; umbones straight, placed considerably to one side ; 

 shorter side well rounded, the other considerably acuminated ; 

 hinge with a broad, triangular, slightly hollow tooth in both 

 valves; inside white. 



Found at Plymouth, South Devon, and at several places on 

 the Irish coast. 



6. Thracia truncata, pi. XLII, f. 28. 

 Anatina truncata, Turton, Biv., p. 46, pi. 4, f. 6. 



Shell convex, cuneiform, subquadrangular; anterior side des- 

 cending in an acute angle from the umbones, which are situate 

 near to that side; posterior side long, with the superior or hinge 

 line very flat, and abruptly truncated ; basal margin nearly- 

 parallel; surface pale yellowish-brown, transversely striate; teeth 

 projecting somewhat obliquely inwards. 



Found in the interior of rocks at Torbay. 



7. Thracia brevirostra, pi. XLIV, f. 11, 12, 13, 14. 

 Anatina brevirostra, Brown, Edin. Journ. Nat. and Geo. 



Science, I, p. 11, pi. 1, f. 1, 2, 3, 4; Ncera brevirostra, Gray. 



Shell very convex, transversely oblong-ovate ; posterior side 

 rounded ; anterior side abruptly tapering to an acuminated, 

 abbreviated beak; umbones small, pointed, and slightly inflected 

 towards the anterior side ; exterior surface covered with a rich 

 fawn-coloured epidermis, with a slight metallic lustre, beneath 

 which the shell is provided with nearly obsolete, transverse 

 striae ; hinge with one large, elevated, recurved, cardinal tooth 

 in the right valve, which fits under the edge of the superior 

 margin in the left ; cartilage fixed in central pits beneath the 

 umbones; inside pale purple, darker towards the extremities; 

 margins plain. Length three-eighths of an inch ; breadth up- 

 wards of half an inch. 



This interesting species was discovered in the Frith of Forth, 

 by James Gerard, Esq.; and I afterwards met with it near Port 

 Seaton. It is also said to have been found on the Northum- 

 berland coast. 



Genus 38 Lepton. — Turton. 



Shell compressed, transversely elongated, or nearly orbicular, 

 cquivalve, and slightly inequilateral, gaping a little at the sides; 

 umbones nearly central, and very slightly inflected ; hinge of 

 one valve witli a central, erect, primary tooth, situate between 

 two hollows, from both sides of the hinge emanate a nearly 

 straight, transverse rib, lying a little way within the margin, 

 upon each of which rests a small tooth-like process, not very 

 remote from the hinge, the rib on one of the sides is furnished 

 with a small, internal, oblique, spoon-shaped cavity ; the other 

 valve is destitute of primary teeth, but with a large, central, 

 triangular hiatus for the reception of the tooth of the opposite 

 valve ; on each side of which are lateral teeth, cleft their whole 



