THE NAUTILUS. 137 



but is smaller, the anterior part of the mussel is much smaller, and 

 the cardinal teeth are markedly different, as seen in quite a number 

 of specimens. 



Pisidium nevadense, n. sp. Mussel inequipartite, oblique, higher 

 in front of the beaks than behind, medium inflated ; superior and 

 posterior margins little curved with a rounded somewhat over right 

 angle between them, inferior rather long, somewhat descending 

 toward the rounded anterior end, supero-anterior slope somewhat 

 curved ; beaks nearer the posterior end, medium large, rounded, 

 slightly prominent over the hinge margin ; scutum and scutellum 

 barely marked ; surface somewhat shining, with slight irregular 

 stria? and a few slight, impressed lines of growth ; color : straw, 

 shell subtranslucent, rather strong ; hinge curved, medium stout, 

 plate rather broad ; cardinal teeth rather large, the right with the 

 anterior part somewhat thickened, the posterior much thicker, with 

 a deep groove, nearly bifid, left anterior long, angular-curved, pos- 

 terior long curved, oblique, extending forward well beyond the apex 

 of the anterior ; laminse little projecting inward, cusps short, pointed, 

 especially those of the left valve ; ligament and resilium rather long, 

 moderately strong. Long. 6, alt. 4.8, diam. 3.3 mm. (100 : 80 : 55). 



Hab.: Nevada Co., California ; types no. 56278 in the National 

 Museum, and my collection no. '2726 ; of the former, one specimen 

 is 6.4 mm. long. For my specimens J am indebted to the late 

 R. E. C. Stearns, being identical with those of the National 

 Museum, which were received from (and collected by ?) J. J. Rivers. 

 Evidently distinct from all described species, but the specimens were 

 shelved in the hope of getting additional material. This Pisidium 

 has the best-formed cardinal teeth of any seen. 



P. (nevadense var., or sp.?) modicum, n. Mussel of similar ap- 

 pearance, but smaller, less oblique, not higher in front of the beafcs 

 than behind, beaks somewhat broader, color more whitish ; long. 4.3, 

 alt. 3.5, diam. 2.6 mm. 



Hab.: White Pine, Nevada. Specimens are in the collection of 

 Mr. B. Walker, from the Wetherby collection, and my collection 

 no. 5813, part of the original lot; more are probably in other col- 

 lections. 



P. glabellum, n. sp Mussel small, somewhat oblique, rather well 

 inflated ; superior margin nearly straight, bounded by angles in front 

 and behind, supero-anterior slope nearly straight, anterior end 



