THE NAUTILUS. 141 



Remarks: This species was at first thought to be Lymnaa sono- 

 maensis Hemphill, but a comparison with that species shows that the 

 present species differs not only from sonomaensis,\^ui from all related 

 species in the form of the spire and aperture. The first two whorls 

 of the spire are coiled in the same plane, producing an abruptly trun- 

 cated appearance. The inner lip is triangular and not evenly 

 rounded as in techella and its varieties, but similar to that of buli- 

 moides, from which it differs in its truncated spire. The only form 

 likely to be confounded with hendersoni is sonomaensis, which differs 

 in the form of the spire and inner lip. 



I take great pleasure in dedicating this interesting species to 

 Judge Junius Henderson, of the University of Colorado. 



SPH.ERIUM PILSBRYANUM, N. SP. 



BY V. STERKI. 



Mussel large, high, inequipartite, oblique, well inflated; beaks 

 rather large, rounded, prominent, inclined towards the anterior; 

 upper margin strongly and regularly curved in the adult, less so or 

 nearlv straight in young specimens, ventral margin rather well and 

 regularly curved; anterior part of the mussel much smaller than the 

 posterior, its outlines rounded or slightly truncate, posterior rounded 

 or truncate obliquely, the end rather drawn downward, rounded or 

 subangular; surface with rather coarse to medium, sharp, concentric 

 striae, regular over the beaks, less so over the balance of the valves, 

 and with about six to eight impressed lines of growth, deepest pos- 

 teriorly, with the interstices somewhat bulging; color chalky-whitish 

 to light or deep gray, in some specimens with alternate zones of light 

 and dark; shell thick; muscle insertions slightly marked, large, not 

 impressed; hinge strong, plate moderately broad, rather long; car- 

 dinal teeth small, rather typically to irregularly formed, the poste- 

 rior of the left valve often wanting or rudimentary; laterals rather 

 large, those of the right valve projecting inward, those of the left 

 only slightly so; anterior short, the left raised cusp-like, the posterior 

 all rather long, not raised to cusps. 



Long. 18, alt. 16, diam. 11-12 mm.; average; the largest, 21 mm. 

 long. 



