CARBONIFEROUS AGE. 15 



characters by which it can be separated from that species; at any rate by the 

 figures and descriptions we have yet seen. Still it is not improbable that a direct 

 comparison with specimens of the Russian species would enable us to point out 

 characters by which they could be distmguished. At one time we supposed that 

 some ventricose specimens found by us in Kansas, might be separated as a variety 

 from the more common slender forms ; but further comparisons have satisfied us 

 that they cannot be regarded as a sufficiently marked variety to make it desirable 

 to designate them by a different name, there being every gradation between these 

 two extremes. In case they should all, however, prove to be distinct from Fischer's 

 species, the name ventricosa may be retained for the American type. 



Locality and position. — The species here described ranges from Ohio to Kansas 

 and southwestern Nebraska, and south to Texas. It seems to be more common, 

 however, west of the Mississippi than east of it, and we have no knowledge of its 

 existence east of Ohio. It probably occurs in western Kentucky, though we have 

 never seen specimens of it from that State. It is common in portions of Missouri. 

 At aU the localities mentioned, it is found only in the Coal Measures. 



The specimens here figured and described are from Juniata, on Kansas River, 

 Kansas, where it occurs in great numbers. 



