266 NEW UNIONIDiE, MELANID^, ETC., 



fliited, with divergent folds at the tips ; ligjiment small and very dark ; epidermis 

 greenish-brown, without rays and with very indistinct marks of growth ; umbonial 

 slope inflated and rounded ; posterior slope narrow, elliptical, with an indistinct im- 

 pressed line in each valve ; anterior cicatrices confluent, rather small and slightl}' 

 impressed; posterior cicatrices confluent, large and very slightly impressed; dorsal 

 cicatrices in a row across the centre of the cavity of the beaks ; cavity of the shell 

 shallow and wide ; cavity of the beaks very shallow and rounded ; nacre bluish 

 white and iridescent. 



Soft -parts. — Branchial uterus occupies nearly the whole width of the inner branchice, 

 the ovisacks being long, closely approximate and filled witli nearly mature embryonic 

 shells ; ova were found in the ovaries also. BrancJiice rather large, rounded below, 

 inner ones much the larger, united the whole length of abdominal sack. Palpi 

 rather small, somewhat thin, oblique, rounded below and united a small distance on 

 the posterior superior edges. Mantle thin, slightly thickened at the edges. Branchial 

 opening rather small, with numerous small, brownish papillae. Anal opening small, 

 without papillte and entirely separated from the branchial opening. Has no super- 

 anal opening ; color of tlie mass dirty white. 



J^mbj't/onic shell suhiriangula,r, \\gh.t brown; dorsal line rather long and straight; 

 side margins irregular and unequal ; one being a segment of a circle, the other an ir- 

 regular curved line, forming an obtuse angle at the base ; basal margin obtusely an- 

 gular and furnished with hooks; granulate over the whole surface. Plate 34, fig. 80. 



Remarks. — There were two only of this species, both in alcohol; male and female. 

 The female fortunately had the embryonic shell nearly matured, and that presents to 

 us a unique and very peculiar form in having unequal lateral margins, as described 

 above. It therefore has the appearance of being abnormal and lapsided. No irregu- 

 larity approaching to this has been observed by me in the numerous North American 

 species which I have examined. 



In oViilmQ peculiaris is near to Bengalensis (nobis), but in other respects it is very 

 different, having divergent folds on the beaks, a white and thicker nacre, etc. Of all 

 the South American species with which I am acquainted, it most nearly resembles 

 Wymanii (nobis), but may easily be distinguished by its darker ej^idermis, its greater 

 inflation and in being a smaller species. There is a slight indication of triplication of 

 the cardinal tooth of the left valve in both the specimens, 



Unio rugososulcatus. pi. 34, fig. 81. 



Testa sulcata, triangulari, subinflata, subasquilaterali, postice biangulata, antice oblique rotundata; 

 valvulis percrassis, antice crassioribus ; natibus prorainentibus ; epidermide olivacea, rugoso-sulcata, 

 obsolete radiata ; dentibus cardinalibus crassis, rugosis, elevatis ; lateralibus sublongis, subcrassis, 

 lamellatis subcurvisque ; margarita argentea et iridesceute. 



