124 oakbonifekous period. 



Fai^iily STROPHOMENID^. 



Genus HEMIPKONITES Pauder, 1830. 

 Hemipronites crinistria Phillips, sp. 



Plato X, fig. 9 a. 



One of the most commou fossils found in the rocks of the Carboniferous 

 period in IlHnois, Missouri, Iowa, Nebraska, and Kansas is a very variable 

 shell that has during the past few years been generally refen-ed to Hemipro- 

 nites crassus Meek and Hayden. After the first publication of their descrip- 

 tion of this species in the Proceedings of the Academy of Natural Sciences 

 of Philadelphia, for 1858, they expressed great doubt (Paleontology of 

 the Upper Missouri, 1864), whether it is really different from H. crinistria 

 Phillij)s {sp.) of Europe. The genus Hemipronites is also freely rep- 

 resented by different varieties in the Subcarboniferous strata of the States 

 just named, so far as they exist there. After long study of these forms, 

 from the strata of both periods, I have failed to discover entirely satis- 

 factory grounds for the specific discrimination of more than one group. 



While I am not prepared to deny that there may be more than one 

 species of Hemipronites among those hitherto described from the various 

 strata referred to, I have at present very little doubt that the species long 

 known as H. crassus ranges through all the strata of both the Subcarbon- 

 iferous and Carboniferous periods in the States before named, and that the 

 species is identical Avith H. crinistria Phillips. The reader is referred to the 

 following works for descriptions and illustrations of most of the varieties of 

 Hemipronites that have been published from strata of the Carboniferous age 

 in America: — Geology of Iowa, Hall, vol. i, part ii,. 1858 ; Paleontology of 

 the Upper Missouri, Meek and Hayden, 1864; Transactions of the Chicago 

 Academy of Sciences, vol. i, part i, 1867; United States Geological Survey 

 of Nebraska, 1872 ; and Carbonformation und Dyas in Nebraska, Geinitz, 

 1866. 



Position and locality. — Strata of the Carboniferous period: — Meadow 

 Creek, south of Fillmore ; Star district, Picacho range ; North Fork of 

 Lowiston Canon, Oquirrh range ; below Ophir City ; Kanab Canon, 



