Logan.] The Invertebrates, Niobrara Group. 491 



This description is made from two incomplete specimens col- 

 lected from the Niobrara outcrops north of Ellis, in Ellis county. 

 It occurs in the lowermost horizon of the Pteranodon beds, 

 where it occurs associated with I. platinus and I. truncatus. 



There exists a striking similarity between this species and the 

 description of Inoceramus broiunii described by Professor Cragin, 

 and it may be that the form just described is a synonym of the 

 latter. But there are certain points of difference, such as the 

 absence of transverse grooves on the hinge line, and compressed 

 teeth on the distal portion of the umbonal cavity in the former. 

 As no figure accompanied Professor Cragin's description of I. 

 brownii, I am unable to decide definitely as to whether they are 

 synonyms or not. The two forms occur in different horizons, 

 Inoceramus eoncentricus occurring in the Pteranodon horizon, and 

 I. brownii occurring in the Fort Hays limestone horizon. 



Inoceramus platinus, n. sp. Plate cxvi. 



Description : Shell large, thin, flat, oblong oval ; hinge mar- 

 gin long, straight, smooth, marked by shallow pits or undula- 

 tions, not concentric, and not regular as in Inoceramus eoncentricus. 

 Body of the shell is thin, and increases but slightly in thickness 

 toward the hinge. Shell substance fibrous and the surface some- 

 what striated, striations giving a banded appearance to the shell 

 in some specimens. Umbonal region slightly depressed ; cavity 

 broad, shallow. Length of longer diameter of adult specimen, 

 from three to four feet ; height, from one and one-half to two 

 feet. 



Fragments of this shell are numerous throughout the Ornith- 

 ostoma beds, but on account of the extreme fragility of the 

 shell whole specimens are difficult to obtain. I have described 

 the species as seen in the field and from fragments collected for 

 the University collection. I have often found adult specimens 

 of this shell exposed by the weathering of the chalk, but, upon 

 attempting to remove them with the means at hand, they would 

 be broken up into so many fragments as to make restoration 

 next to impossible. Two large fragments of this shell in the 

 University collection measure more than eighteen inches in 



