CONCHOLOaiCAL ■WRITINGS. 83 



9 N. G. DIPLASMA. 



Shell inequilateral and transversal, hinge with two lamellar teeth, 

 nearly confluent, united into a curve, not serrulate, more or less 

 unequal, bilamellar anteriorly in the right valve, bilamellar poste" 

 riorly in the left valve. 



Certainly a distinct Genus, more like Gyclas and Hiria, in the' 

 hinge than Unio, although so labelled by Dr. Burroughs and our 

 conchologists, by the external form merely. I suspect that many 

 Asiatic Unios belong to it. I shall describe 3 of them, besides our 

 doubtful American species. 



114 Sp. Diplasma marginata. Shell thin, elliptical, swelled, 

 back horizontal, sloping and truncate obliquely behind ; outside 

 very smooth, shining brown, anterior and interior margin yellowish, 

 inside pale incarnate. Length one half, diameter 1-3, axis 3-10 Of 

 the breadth. 



From the river Tennessee, as stated to Mr. Hembel, but so near 

 the next, that the fact appears doubtful to me ; perhaps the locality 

 has been erroneously stated or labelled in Mr. Lea's cabinet, from 

 whence the shell is said to have come, and it may be also a shell 

 from Hindostan. Lamellar tooth properly curved, the anterior 

 pretty long. Size of the shell over two inches. 



115 Sp. Diplasma similis. Shell very thin, elliptical, not swelled, 

 back horizontal, truncate obliquely behind, hardly sloping, outside 

 smooth, dark olivaceous, with a pale margin, inside bluish incarnate. 

 Length T-IS, diameter 4-15, axis 1-5 of the breadth. 



From the river Ganges, so similar to the last as almost to appear 

 the same, yet thinner, flatter, and teeth somewhat different, forming 

 almost an angle rather than a curved arch, anterior tooth shorter, 

 oblique, the posterior perfectly horizontal. Length nearly two 

 inches. 



116 Sp. Diplasma vitrea. Shell very thin and brittle, almost 

 transparent, oval swelled, broader behind, with a slope outside, very 

 smooth, greenish, or fulvescent, inside whitish, teeth subequal. 

 Length 2-3, diameter 2-5, axis 2-5 of the breadth. 



From the river Jellinghy in Bengal. Small, hardly over one inch, 

 fine delicate shell. 



IIT Sp. Diplasma striata. Shell thick, suboval, swelled, behind 

 sloping subtruncate and transversally striated, outside olivaceous 

 greenish, smooth below, but longitudinally striated above ; strias in 



