18 



Chouteau uot referable to either of the above named genera, belong 

 to Pernopecten, which ranges from the Chouteau to the Coal 

 Measures, and Grammysia, which ranges from the Upper Silurian 

 to the Chouteau. 



The position of the Chouteau, at the base of the Subcarboni- 

 ferous System and above the Devonian, is well established, by its 

 crinoidal fauna; but the Lamellibranchs, as above set forth, furnish 

 additional evidence of its place in the geological column, that can- 

 not be misunderstood by any paleontologist. We have seen frag- 

 ments, too poor for specific description, from . the Chouteau, be- 

 longing to four other genera of Lamellibranchs, which further 

 support the conclusion derived from those above described. 



CLASS GASTEOPODA. 

 OEDEE BEANCHIFEEA. 

 Family PLEUEOTOMAEIID.E. 



MURCHISONIA INDIANENSIS, n. sp. 



Plate II, Fig. 31, lateral view, part of the shell is preserved 

 and a little of the surface ornamentation; Fig. 32, 

 part of surface magnified. 



Species very large. Shell elongated so as to be from one-fourth 

 to one-third higher than wide. Volutions five or six. Only three 

 volutions are preserved, in our specimen, but, at least, two are 

 broken away. The last volution is sharply angular at the pe- 

 ripheral band, those toward the apex obtusely angular. The body 

 whorl is rounded below, and slightly concave, from the suture to 

 the peripheral angle. The concave depression is more strongly 

 marked on the volutions toward the apex, between the suture and 

 the periphery. Umbilicus open. Aperture subquadrate, about a 3 

 high as wide, notched at the periphery. Suture canaliculate. 

 Surface marked by fine strife directed gently backward from the 

 suture. No revolving ridges. 



This species is readily distinguished by its large size, general 

 form, angular whorls, subquadrate aperture, open umbilicus and 

 surface ornamentation. We do not know of any nearly related 

 species. 



Found by Geo. K. Greene in the Knobstone Group, at New 

 Albany, Indiana, and now in the collection of Wm. F. E. Gurley. 



