CONCHOLOGICAL 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 Cyclas 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 haif, 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 7-15, 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. 
117 Sp. Diplasma striata. Shell thick, suboval, swelled, behind 
sloping subtruncate and transversally striated, outside olivaceous 
greenish, smooth below, but longitudinally striated above ; strias in 
