PALEONTOLOGY OF IOWA. 709 



FOSSILS OF THE COAL MEASURES. 



IN the selection of a few species of fossils characteristic 01 

 the Coal measures, I have made no attempt to indicate those 

 of the upper or lower measures, or to carry the discrimination 

 still farther, as I am aware it may most advantageously be 

 done in the determination of the fossils of the successive 

 beds of the series. Such a course would require far more 

 space than I have at my disposal at the present time. The 

 greater proportion of Lamellibranchiata and Gasteropoda 

 given among the Coal-measure fossils is in fact the natural 

 expression of the fauna as it has fallen under my observation. 

 In the Coal measures, and their associated limestones, we 

 find the fossils having a wider geographical distribution than 

 we know in any of the preceding periods. Several species, 

 which are common and characteristic forms in Western 

 Pennsylvania and Ohio, are known in Indiana, Illinois, Iowa 

 and Missouri ; and they have been found at intervals from 

 the most northerly part of the continent explored, throughout 

 the entire extent of the Rocky mountains to New-Mexico. 



Spirifer cameratus. 



PLATE XXVIII. FIG. 2 a, ft. 



Spirifer cameratus : MORTOX, Silliman's American Journal of Science, 1836, Vol. xxtr, 



pa. 150, pi. 2, f. 3. 



Spirifer mevsebacAauvs : RCEXER, Kreid. ron Texas, 1852, pa. 88, pi. 11, f. 7. 

 Spirifer triplicates : HALL, Stansbnry's Report on the Exploration and Surrey of the Val- 

 ley of the Great Salt Lake of Utah, 1852, pa. 410, pi. 2, f. 5 ( by error pi. 4) . 



Spirifer fasciger f KETSEBLIXG : OWES, Report on Wisconsin, Iowa and Minnesota, 1852, 



pi. 5, f. 4. 



Spirifer catneratvs, MORTOX : HALL, in Explorations and Surreys for a R.R. Route from 

 the Mississippi river to the Pacific ocean, 1S56, Vol. iii, pa. 102, pi. 2, f. 9, 12 & 13. 



SHELL transverse, semielliptical, semicircular or subtrigonal 



