Dr. J. E. Gray on some Families of Bivalve Shells, 371 



strongly radiately ribbed ; margin closed, broadly folded ', hinge- 

 area broad, concentrically grooved or smooth ; hinge-teeth 

 oblong, dilated, and with the plates more or less oblique at the 

 outer ends. Periostraca olive, smooth or paleaceous. 

 Marine, or in brackish water. 



a. Periostraca thick, black, smooth ; hinye-area grodved, A.grandis. 



b. Periostraca thick, brown, velvety ; hinge-area smooth. 



A. holosericea. ■ Hinder end produced. , 



A. multicostata, A. globosa. Hinder end square. 

 A. reversa. Hinder slope flattened. 



c. Periostraca thick, brown, velvet-like, with a series of cylindrical 



bristles in the radiating grooves ; hinge-area smooth. Cara. 



* Shell produced behind; hinge-margin short. A. Scapha=A. 



obliqua, A. maculosa. 

 ** Shell broad, notched behind ; hinge-margin produced. A. au- 



riculata = avicularoides. 



d. Periostraca thick, brown, foliaceous, with broad lobes on the 



edge. Rasia. A. formosa, A. secticostata, A. Deshayesii, 

 A. trapezia = lobata, A. antiquata, A. radiata, A. infiata. 



e. Periostraca thick, or moderately thin, smooth, brown ; ribs of 



shell nodulose. A. tuberculosa, A. granosa, A. Corbicula= 

 cuneata. 



9. Scapharca, Gray, Proc. Zool. Soc. 1847. Shell ovate or 

 oblong, subquadrangular, subequilateral, inequivalved, strongly 

 costate ; margin closed, strongly plaited ; left valve rather the 

 largest, with the hinder part of the lower margin produced and 

 receiving the edge of the right valve within it, and marked with 

 deeper plaits ; hinge-area narrow ; teeth subequal, dilated, and 

 with the plate of the outer ends more or less oblique or longi- 

 tudinal. 



a. Shell subcordate. S. cepoides, S. incongrua = rhomboidea 



= Brasiliana=ovata=rufescens = insequivalvis, S. cornea = 

 anomala. 



b. Shell oblong -elongate. S. Japonica=gubernaculum. 



c. Shell subquadrate. S. pertusa. 



B. Shell trigonal, truncated behind; hinder hinge-tooth small, 

 curved, anterior very long, linear. 



10. Noetia, Gray, Syn. B. M. 1840, 155 ; 1844, 92. Shell 



24* 



