CONCHOLOGY. 63 
A. pisolina. A. lactea. 
A. callifera. A. cancellaria. 
A. bisulcata. A. irudina. 
A. senilis. A. rhombea. 
A. auriculata, A. corbicula. 
A. Cayennensis. A. Indica. 
A, antiquata. A. granosa. 
A. Braziliana. A. squamosa. 
A. pistachia. 
A. pounderosa,* A. incongrua.* 
A. pexata.* A. transversa.* 
2. Genus Cucullza. Pl. VIII. 
Animal. As above. 
Shell. Trapeziform, inequilateral, equivalve, heart-shaped ; 
beaks far apart, separated by the angular groove of the ligament, 
which is altogether external; hinge linear, straight, with small 
transverse teeth, having at its extremity from two to five parallel 
ribs ; valves minutely striated longitudinally ; margins crenulated. 
The Cucullea is distinguished from the Arca by the muscular 
impression, to one side of which is an auriform testaceous appen- 
dage; the shell also is more trapeziform. Inhabits the Indian 
ocean. One living species. One fossil. 
Cucullea auriculifera. 
3. Genus Pectunculus. Pl. VIII. 
Animal. Body round, more or less compressed ; mantle with- 
out cirri or tubes; foot securiform, cleft at its inferior anterior 
edge; buccal appendages linear. 
Shell, Orbicular, equivalve, subequilateral; summit nearly 
vertical, and more or less distant; hinge formed upon each valve, 
of a numerous series of small teeth disposed in a curved line, 
sometimes interrupted beneath the summit; ligament as in Arca, 
but usually much narrower. Inhabits the British and Mediterra- 
nean seas. T'wenty-two living species. Nine fossil. 
Pectunculus pilosus. Pectunculus Pennaceus. 
P. marmoratus. P. castaneus. 
