131 



cept on the upper whorls : with twelve spiral prominent cord- 

 like ridges, half of which appear on the spire, decussated by 

 much less prominent regular transverse ridges, with the inter- 

 sections well developed into nodules : apex acute : spire with 

 the outlines moderately curvilinear : whorls five, rather con- 

 vex, with the suture moderately impressed ; last whorl but 

 little ventricose : aperture rather narrow and sinuous ; lip 

 slightly thickened, not denticulate within, (in old shells ?) 

 with the notch of medium size. 



Mean divergence about 40° ; length .145 inch ; breadth 

 .06 inch ; length of aperture .06 inch. 



Of Pleurotoma albella Ad., (Cont. to Conch., p. 63,) a va- 

 riety is wax-colored at both extremities, and has irregular 

 spiral lines of the same on the lower part of the whorls. 



Valvata inconspicua. Shell subdiscoidal : pale horn color ? 

 with the striae of growth microscopic : spire convex, moder- 

 ately elevated : whorls three, very rapidly increasing, with a 

 deep canaliculate suture : aperture large, not much advanced 

 above : umbilicus about half as wide as the penulL whorl. 



Greatest breadth .07 inch ; least breadth .05 inch ; height 

 .04 inch. 



Planorbis HUMiLis. Shell subdiscoidal : color — ? with 

 coarse striae of growth : apex and spire moderately depressed 

 on the right side : whorls two and one-half ; last whorl with 

 a very acute periphery nearly in the plane of the spire, mod- 

 erately dilated around the umbilical region : aperture large, 

 subtriangular, acutely angled at the periphery of the last 

 whorl : umbilical region abruptly excavated, with the conca- 

 vity about two-thirds as wide as the last whorl. 



Greatest breadth .06 inch ; least breadth .045 inch ; height 

 .025 inch. 



