Mactracea.] 



MOLLUSCA. 



1 fl- 



are separated by a triangular hiatus, below the umbo; inside 

 glossy, white. Length a little more than a quarter of an inch ; 

 breadth nearly half an inch. 



Found at Belton Sands, near Dunbar ; and Turton says it 

 inhabits the Western coasts. 



5. Tellimya glabra, pi. XLII, f. 20, 21. 

 Tellimya glabra, First Ed., pi. 14, f. 20, 21. 



Shell elliptical, moderately inflated, thin, smooth, extremely 

 glossy; umbones obtuse, placed considerably to one side; shorter 

 side obliquely subtruncated, the other rounded; hinge with one 

 broad primary tooth in each valve, and a large hiatus immedi- 

 ately under the umbones in both valves; inside smooth, glossy; 

 margins sharp. Length nearly a quarter of an inch ; breadth 

 about half an inch. 



Found by General Bingham, at Dunbar; in his cabinet, and 

 also that of Lady Jardine. 



6. Tellimya bidentata, pi. XLIV, f. 8, 9- 



Anatina bidentata, First Ed., pi. 11, f. 8, 9; Montacuta 

 bidentata, Turton, Biv., p. 60; Mya bidentata, Montagu, p. 44, 

 pi. 2, f. 5 ; Brown, Ency. Brit., VI, p. 405. 



Shell suboval, thin, compressed, smooth, white, but not 

 glossy ; umbones small, situate nearest to one side, and slightly 

 bent; hinge with two broad, erect, laminated teeth in one 

 valve, these stand obliquely outwards from the beak, and some- 

 what distant from each other, between these, and immediately 

 under the umbo, is a slight triangular cavity for sustaining the 

 cartilage ; opposite valve with a triangular hiatus, situate imme- 

 diately below the umbo, for the reception of the opposite teeth. 

 Length an eighth of an inch ; breadth rather more. 



Found in Salcomb Bay, burrowing in decayed thick oyster 

 shells. 



7. Tellimya substriata, pi. XL, f. 23. 



Tellimya substriata, First Ed., pi. 16, f. 23 ; Montacuta sub- 

 striata, Turton, Biv., p. 59, pi. 11, f. 9, 10; Ligula substriata, 

 Montagu, Sup., p. 25. 



Shell subovate, somewhat oblique, a little inflated, slightly 

 contracted in the middle of the valves, subpellucid, white, 

 sometimes with a ferruginous tinge ; umbones prominent, 

 straight, and not quite central ; one side short and narrowed, 

 the opposite ample and rounded; surface covered with elevated, 

 distant, nearly obsolete strise ; hinge with a cleft side tooth, a 

 narrow grooved tooth on the opposite side, and a hiatus 

 between them, immediately under the umbo; teeth in the 

 opposite valve very indistinct, if any, with a central triangular 

 hiatus. Diameter about the tenth of an inch. 



Found attached to corallines, on the Devonshire coast; and 

 to spines of the Echinus purpureas, to which they are attached 

 by slender filamentary processes, emanating from the middle of 

 the margin. 



Section III. — Ligament internal; shell gaping at the sides. 



Genus 34 — Mactra. — Linnaeus. 

 Shell generally thin, sometimes thick; equivalve, for the most 

 part nearly equilateral, and more or less regularly triangular ; 

 slightly gaping at one end, and almost imperceptibly so at the 

 other ; each valve with one V shaped cardinal tooth, the point 

 being next the umbo, diverging from it, and in some species 

 >he limbs are disunited at the base, so as to give the appearance 



of two distinct teeth ; close on the posterior side is situate a 

 very thin, sharp tooth ; immediately behind the angular tooth 

 is placed the pit for the reception of the ligament, and project- 

 ing somewhat within the shell; one valve with two lateral teeth 

 on each side, and one on both sides in the other, diverging from 

 the beaks, near the margin of the shell, and fitting into the 

 space between the two in the opposite valve ; two lateral, 

 remote, muscular impressions ; pallial impression with a small 

 sinus; ligament consisting of two portions, the one considerably 

 larger than the other and internal, and the other half external ; 

 two strong, lateral, muscular impressions in each valve ; pallial 

 impression interrupted by a small sinus. 



Section I. — Lateral teeth smooth ; shell fragile. 



1. Mactra glauca, pi. XLI, f. 1. 



Mactra glauca, First Ed., pi. 15, f. 1 ; Montagu, p. 571 ; 

 Donovan, IV, pi. 125 ; Turton, Biv., p. 73 ; Fleming, p. 428 ; 

 Mactra helvacea, Lamarck, V, p. 473. 



Shell subtriangular, thin; anterior side slightly wrinkled; 

 umbones somewhat obtuse, a little reflected, with a narrow 

 intervening gap ; surface of a cream-yellow colour, very finely 

 striated transversely, and with irregular, broad and narrow glau- 

 cous radiations of a pale brown-colour ; inside of a pale cream- 

 colour, or purple ; margins thin, and sharp. 



Found on the coast of Cornwall ; but I am not aware that 

 any living specimens have been met with, the locality not 

 having been yet detected. 



2. Mactra Stultorum, pi. XLI, f. 2. 



Mactra Stultorum, First Ed., pi. 15, f. 2 ; Montagu, p. 94 ; 

 Donovan, III, pi. 106; Turton, Biv., p. 72; Maton and Rackett, 

 p. 69. 



Shell subtriangular, thin, semipellucid ; umbones central, 

 rather prominent, and frequently of a purplish hue; sides nearly 

 equal; surface covered with a yellowish-brown, or fawn-coloured 

 epidermis, frequently of a cream-colour, beneath which the shell 

 is elegantly radiated with deeper brown, or brownish-purple, 

 irregular in number, some broad, others narrow, and frequently 

 with transverse zones of a paler colour ; inside pale lilac, which 

 frequently penetrates to the outside, giving it the same cast of 

 colour ; when the epidermis is removed, it is found to be 

 covered with faint, somewhat irregular, transverse stria?. Vary- 

 ing in length from an inch and a half to nearly two inches; and 

 in breadth from one inch and three-quarters to nearly two 

 inches and a half. 



This species is found on most of the British and Irish coasts. 



Some specimens are entirely destitute of rays. 



3. Mactra dealbeta, pi. XLI, f. 8, 9. 



3Iactra dealbeta, First Ed., pi. 15, f. 8, 9 ; Pulteney, Cat. 

 Dorset, p. 31 ; Montagu, p. 95, pi. 5, f. 1 ; Maton and Rackett, 

 p. 68, pi. 1, f. 10 ; Fleming, p. 429. 



Shell transversely ovate, thin, fragile, moderately inflated ; 

 umbones not quite central, but situate nearer the larger side ; 

 gaping a little at the narrower side; colour grayish or brownish- 

 white, very finely striated concentrically, and with a few coarser 

 transverse wrinkles; middle tooth in one valve broad, cleft, and 

 angulated close to the beak ; lateral teeth not very remote ; 

 inside glossy, white ; margin plain, with a sharp edge. 



Found at Weymouth, by Mr. Bryer, but is extremely rare ; 

 if it is not merely a variety of M. Stultorum. 



