270 NEW UNIONIDiB, MELAN1D.E, ETC., 



which give the surface a rugose character. There is also a slight emargination at the 

 posterior basal margin which may not pertain to all other specimens. 



Ukio acutirostris. pi. 35, fig. 84. 



Testa Isevi, oWonga, ad latere eompressa, valde inrequilaterali, postice obtuse angulata, antice tnmcata ; 

 valvulis crassiusculis, antice crassioribus ; natibus prominulis ; epidermide tenebroso-fusca, 

 nigrescente, eradiata ; dentibus cardinalibus parviusculis, in utroque valvule sulcato-divergente ; 

 lateralibus prrelongis, aliquanto eurvatis granulatisque ; margarita alba et valde iridescente. 



Shell smooth, oblong, compressed at the sides^ very inequilateral, obtusely angular 

 behind and truncate before; valves somewhat thick, thicker before; beaks somewhat 

 23rominent ; epidermis dark brown, nearly black, without rays ; cardinal teeth rather 

 small, in both valves sulcate and divergent ; lateral teeth very long, curved and 

 granulate; nacre white and very iridescent. 

 Proc. Acad. Nat. Sci. 1866, p. 34. 



Hah. — South America, Don Patricio M. Paz. 



My cabinet and cabinet of Don P. M, Paz. 

 Diam. 1, Length 1-6, Breadth 2-4 inches. 



Shell smooth, oblong, compressed at the sides, very inequilateral, obtusely angular 

 behind and truncate before ; substance of the shell somewhat thick, thicker before ; 

 beaks somewhat prominent; ligament long, tliin and very dark brown; epidermis 

 dark brown, nearly black, somewhat striate, with distant marks of growth; umbonial 

 slope long and obtusely angular ; posterior slope long, compressed at the sides and 

 somewhat carinate; cardinal teeth rather small, in both valves sulcate and 

 divergent ; lateral teeth very long, curved and granulate ; anterior cicatrices con- 

 fluent, rather small and well impressed; posterior cicatrices confluent, I'ather large 

 and slightly impressed ; dorsal cicatrices placed across the centre of the cavity of the 

 beaks ; cavity of the shell shallow and very wide ; cavity of the beaks very shallow ; 

 nacre white and very iridescent. 



Soft Parts. — Branchial uterus occupies nearly the whole width of the inner branchia, 

 the ovisacks being somewhat long, closely approximate and filled with ova which ap- 

 pear to be elliptical and not matured. Ova were also found in the ovaries. Branchice 

 very long, the outer one curved, the inner nearly straight at the basal margin and 

 much the larger, united the whole length of the abdominal sack. PaJpi large, rather 

 thick, round below and united only at the upper edges. Mantle thin, slightly 

 thickened at the edges. Anal opening rather large, without papilla} and entii'ely 

 separated from the branchial opening. No super-anal opening. Color of the mass 

 dirty white. 



Itema.rlcs. — This was a single female specimen of a species interesting from its un- 

 usual outline. The ova were not sufliciently advanced to give one an idea of the 



