AMPHIDESMA. CONCHIFERA. 107 



ly gaping, and transverse waved striae ; anterior side elongated, 

 angulated. 1^ inch broad. Seas of New Holland. Lam. v. 495. 



C. nucleus, Lam. (M. incequivalvis, Mont.) Shell somewhat trian- 

 gular, gibbous, transversely striated, the valves very unequal ; 

 beaks prominent ; epidermis brown ; shell whitish. 4 lines long, 

 5 broad. Inhabits coasts of Britain, not uncommon. B. Brown's 

 Illust. pi. 14, fig. 6-9. 



Fossil species of this genus are found on the Continent near Paris, and in Bri- 

 tain in cnig, green-sand, and London clay. 



FAMILY IV. MACTRAC^A. 



Shell equivalve, often gaping at the lateral extremities ; liga- 

 ment interior, or partly external ; animal with the foot small 

 and compressed. 



1. Ligament seen externally , or double. 



Gen. 41. AMPHIDESMA, Lam. 



Shell transverse, inequilateral, suboval or rounded, sometimes 

 slightly gaping on the sides ; hinge with one or two teeth and 

 a narrow groove for the interior ligament; ligament double; the 

 external one short, the internal fixed on the primary grooves. 



A. lucinalis, Lam. (Tellina lactea, Gmel.) Shell suborbicular, gib- 

 bous, pellucid, smooth; groove of the ligament narrow and oblique. 

 i inch long. Inhabits European seas. Chem. vi. pi. 13, fig, 125. 



A. Boysii, (Mactra, Mont.) Shell white, pellucid, subtriangular, 

 ovate, compressed, and glabrous ; hinge with lateral teeth in only 

 one valve. ^ inch long, f broad^ B. Wood, Lin. Trans, vi. pi. 18 

 fig. 9-12. 



A. prismatica, Lam. (Ligula, Mont.) Shell oblong, white, glossy* 

 attenuated at one end, obsoletely striated concentrically ; hinge 

 with a somewhat spoon-shaped tooth. 3 lines long, and nearly 

 twice as broad. British coasts. B. Browns Illust. pi. 14, fig. 5. 



Gen. 42. SOLEMYA, Lam. 



Shell inequilateral, equivalve, elongated transversely, obtuse at 

 the extremities, with the epidermis shining ; beaks scarcely 

 distinct ; one primary tooth in each valve, dilated, compres- 

 sed, very oblique, slightly concave above, receiving the liga- 

 ment ; ligament partly external, partly internal. 



S. Australia, Lam. Shell oblong, fuscous, shining, radiated ; valves 

 near the umbo emarginate. 2 inches broad. Inhabits seas of 

 New Holland Lam. v. 489. 



S. Mediterranean Lam. Shell oblong, fuscous, shining, radiated with 

 yellow ; valves entire at the umbones. Inhabits Mediterranean 

 sea. Lam. v. 489. 



Gen. 43. UNGULINA, Lam. 

 Shell longitudinal or transverse, rounded above, almost equila- 



