49 



with the species herein described. First, however, we must call 

 atteutiou to the fact that Meek also mistook the base for the sum- 

 mit, and his definition must be corrected in that respect, and bis 

 figure 2o must be regarded as the base instead of the summit, and 

 figure 2b must be reversed end for end. The fact too, that our 

 specimen is much lai-ger than any that either Prof. Hall or Prof. 

 Meek mentioned, is immaterial. 



Our specimen is convex at the base, and not umbilicated or con- 

 cave as R. globularis is described. Our specimen does not possess 

 the transversely elongated rhomboidal apertures found in li. glo- 

 bularis. And the rows of rhomboidal depressions, in R. globu- 

 laris, as shown in the illustration 26, do not pass half way around 

 the skeleton, while in our species they pass around the skeleton 

 and nearly half around again. The two species, therefore, seem 

 to be widely sepai'ated from each other, though they occur in rocks 

 of the same geological age. 



It may be proper here to remark, that some European authors 

 widely class Americao fossils in lists of syfionyms with European 

 fossils and with fossils belonging to different geological formations, 

 in America. As an illustration, we find R. globularis, which is 

 known only from the Galena Group, in the Lower Silurian, and 

 R. ohioensis, and R. sublurbuudtis which are known only from the 

 highest members of the Niagara Group, classed by one of those 

 authors as synonyms for IschadHes koenigi. It would seem that 

 some of them have no idea of the order of the geological forma- 

 tions in America, and are equally as obscure in making compari- 

 sons of fossils. No species of fossils, animal or vegetable, was ever 

 found common to the Galena and Niagara Groups, and there does 

 not seem to have been any excuse for confounding R. globularis with 

 R ohioensis of Meek, or R. subturbinatus of Hall, on any paheon- 

 tological grounds or even upon faociful resemplance. Neither is 

 there anything in the descriptions or illustrations of R ohioensis 

 by Meek, and R. subturbinatus by Hall, that would indicate that 

 they might be synonyms. It will be noticed that Meek, in Ohio 

 Palaintology, Vol. 2, and Hall, in the 11th Report of the Geologi- 

 cal Survey of Indiana, continue to call the base, the summit of 

 —7 



