18 



Chouteau not referable to either of tht above named genera, belong 

 to Fernopecien, which ranges from the Chouteau to the Coal 

 Measures, and Grammysui, which ranj^es from the Upper Silurian 

 to the Chouteau. 



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

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

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

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

 not be misunderstood by any pala-ontologist. 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 GASTROPODA. 



ORDEK BRANCHIFERA. 



Family PLEUROTOMARIID.E. 



MURCHISONIA INDIANENSIS, D. sp. 



Plate IT, Fig. 31, lateral view, part of the slicll is preserved 



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



part of surface magnijied. 



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

 to one-third higher than wide. Volutions live 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 Ijelow, 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 as 

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

 Surface marked by fine 8tri;e directed gently backward from the 

 suture. No revolving ridges. 



This species is readily distinguished by its Urge size, general 

 form, angular whorls, subquadrate aperture, open umbilicus and 

 surface ornamentation. We do not kuow of any nearly related 

 species. 



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

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



