GEOLOGY OF SOUTHWESTERN IOWA 535 



splendens and P. wabashensis were for years afterwards gen- 

 erally identified as P. longispinus Sowerby. iNleek in the Final 

 Report on Nebraska, following Davidson, referred, though doubt- 

 fully, the Nebraska species to P. longispinus, at the same time 

 stating that it was identical with P. wabasliensis N. & P. Stuart 

 Weller in Carboniferous Invertebrates, Bulletin 153, U. S. Ge- 

 ological Survey, gives P. splendens as synonym of P. longispinus 

 and gives full generic value to P. luabasliensis. The writer in 

 the past has endeavored to follow Weller in identifications. With 

 the usual imperfect material found it seems impossible to dis- 

 criminate these two species. Although the extremes can be dif- 

 ferentiated it is thought they 'merge into one another, and the 

 identification of much the greater number of specimens is largely 

 a matter of personal opinion. It would simplify things greatly 

 if all the Marginifera were referred to M. ivabashensis. The same 

 condition is found with the genus Chonetes where the same spe- 

 cies vary so greatly in the number of the cardinal spines, pro- 

 longation of the ears, and depth of the mesial sinus as to cause 

 difficulty in coming to a decision whether one is dealing with 

 only a variety or with a good species. There is also difficulty 

 with the gastropods as the greater number are found in shale and 

 in an imperfect condition. SpJiaerodoma primogenia has been 

 listed as found in these strata. However, White states in Indi- 

 ana Report for 1883 that this species is without a columnar fold 

 whereas all specimens of Sphaerodoma collected, so far as can 

 be ascertained with rather poor material, have such a fold. Meek 

 in the Final Report on Nebraska refers his species to {Macro- 

 cheilus) S. intercalaris. However, his figiire does not show the 

 aperture and he gives no diagnosis. IMeek and Worthen in a fig- 

 ure in Illinois Paleontology, Volume 2, show this species without 

 a columnar fold. jMost of the specimens can be identified as S. 

 paludinaeformis, leaving much material conjectural, though this 

 may be included in 8. intercalaris. Many small pelecypods are 

 found which can not well be classified, and their identification 

 is fraught with difficulty and is questionable. The writer has 

 been criticised in his identification of Marginifera muricata in 

 the Forbes and City Bluffs. In Bulletin 211 U. S. Geological 

 Survey Girty lists M. muricata as present in the Lecompton and 

 Deer Creek of Kansas. This species or one closely allied to it is 

 present in the Iowa formations. However, the writer does wish 

 to be dogmatic as to the possible species in the genus Margini- 



