37(X Dr. J. Ei Gray on some Fainilies vf Bivalve Shells. 



of the cardinal teeth' are transverse, like the inner ones; in- 

 others they are nearly longitudinal, like the teeth of Cucullcea ; 

 and in others again this part of the tooth is only divided into 

 some ii'regular tubercles, or nearly obliterated. 



I have observed the same variation, but not to such an extent, 

 in other species ; so that the form of the teeth does not afford 

 generic nor even good specific characters. 



.5i CucuUcea, Lamk. Shell ventricose, subquadrate, subequi- 

 lateral, equivalve, radiately striated ; hinder slope subangular ; 

 margin entire, closed beneath; cardinal area narrow ; the cardinal, 

 teeth dilated and bent down at the outer end, and divided into 

 a, few large longitudinal plates. The scar of the hinder adductor 

 muscle on an elevated plate. Periostraca furfuraceous. 



The cardinal area is smooth when the ligament and cartilage 

 are removed, and the ligament appears smooth, but in some 

 specimens I have observed two or three angular grooves. 



Cucull<2a concamerata = C. auriculifera, Lamk. = A. cucullus, 

 Gmelin. 



6. Scaphula, Benson [Scaphura, Gray, misprint). Shell thin, 

 smooth, elongate, subcylindrical, equivalve, inequilateral ; hinder 

 slope elongate, slightly keeled ; margin entire, closed ; cardinal 

 area narrow; hinge-teeth narrow, enlarged at the outer end, and 

 divided into a few broad, oblique, nearly longitudinal laminae. 

 Periostraca thin, smooth. 



Freshwater rivers of India. 



Scaphula Celox, Bens., S. Pinna, Bens. 



B. Shell radiately costated; lower margin strongly dentated, 

 interlocking ; the ligament and cartilage occupying the whole 

 area, smooth or transversely striated. 



A. Shell ohlong, equivalve, subquadrate ; cardinal teeth subequal. 



. 7. Senilia, Gray, Syn. B. M. 1840, 155; 1844, 81 & 92. Shell 

 very thick, subcordate, ovate, equilateral, equivalve, strongly 

 radiately ribbed; cardinal area rather broad, with concentric 

 grooves ; margins closed, very broadly folded ; hinge-teeth large, 

 oblong, nearly similar, divided into large, rugose, irregular cross- 

 plates. Periostraca thin, hard, olive, polished. 



Living in brackish waters of Africa. 



The teeth and the plates into which they are divided are very 

 variable in shape, size, and disposition. 



S. senilis. 



8. Anadara, Gray, Proc. Zool. Soc. 1847, 198. Shell thick, 

 subcordate-ovate or subquadrate, subequilateral, equivalved, 



