CHIEFLY OF THE UNITED STATES. 159 



Planoebis Billingsii. pi. 23, fig. 72. 



Testa Isevi, planulata, superae plano-convexa, subtus lato umbilicata, estriata ; anfractibus quaternis ; labro 

 acuto; apertura grandiuscula, subrotunda, obliqua. 



Shell smooth, flattened, plano-convex above, widely umbilicate below and without 

 striaB ; whorls four ; outer lip acute ; aperture rather large, rounded and oblique. 

 Proc. Acad. Nat. Sci. 1864, p. 111. 



Hah. — Ottawa River, Canada West, E. Billings, Esq. 



My cabinet and cabinet of Mr. Billings. 

 Diam. -18. 



Remarl^s. — Mr. Billings sent me many of this small species some years since. I 

 have never been able to place it with any of the species I know. It is near to parvus, 

 Say, but differs in having a wider umbilicus, in having a more oblique aperture and 

 exhibiting one more whorl. Some specimens, received subsequently from Prof- 

 Daniels, Palmyra, Wisconsin, belong to this species. I have great pleasure in naming 

 it after E. Billings, to whom I am indebted for many shells from Canada. 



Ltmnea Hatdenii. pi. 24, fig. 73. 



Testa ovato-conica, lasvi, tenui, pallido-cornea, imperforata ; spira breviuseula ; anfractibus quinis, con- 

 vexisj suturis valde impressis ; apertura ovata ; columella fortiter plieata. 



Shell ovately conical, smooth, thin, pale horn-color, impei'forate ; spire rather 

 short ; whorls five, convex ; sutures very much impressed ; aperture ovate ; columella 

 strongly plicate. 



Proc. Acad. Nat. Sci., 1858, p. 166. 



Hob. — Yellow Stone and Big Sioux Rivers, Dr. Hayden. 



My cabinet and cabinets of Dr. Hayden and Smithsonian Institute. 

 Diam. -40, Length -87 inch. 



Remarks. — This is about the size of and very closely resembles L. umhrosa. Say, It 

 may, however, be at once distinguished by the inflation of the upper whorls, which 

 are remarkable, their convexity being very great. The body whorl is not so large in 

 proportion as the umhrosa. 



There are three specimens before me, and all these have a mark of growth on 

 the back of the last whorl forming a dark and light band. 



I am indebted to Dr. Hayden for these and many other species which he brought 

 from Nebraska, &c. All the other Lymneo} brought by him were species common to 

 the Valley of the Ohio and of Mississippi. I have great pleasure in naming this after 

 Dr. Hayden, who has done so much for the Natural History and Geology of the far 

 West. 



