614 GEOLOGICAL SURVEY OF IOWA. 



more or less strongly marked by spiniferous nodes, and 

 slightly curved over the anal side. Surface beautifully striate, 

 and sometimes granulose-striate. 



This species differs from the Jlctinocrinus (Dorycrinuts*) mississippiensis of RCEMEK, 

 both in the character of the base and the form of the plates and their surface mark- 

 ings, as well as in the spines, which in that one have a different form, and are re- 

 presented as quite smooth; while such character rarely or never occurs, except from 

 wearing, in the species before us. 



I have before me two very distinct species, from the same rock, bearing spines. 

 One of these, though much smaller, resembles, in the character of its base and ge- 

 neral outline of form, the species of Dr. R<EMER, and is furnished with smooth 

 tapering spines like that one. The other species has the spines running in a direction 

 almost rectangular to the axis of the body, and much shorter and more abruptly 

 tapering than either of those mentioned. 



Fig. 6 a. The anterior side of specimen, showing the base of arms and anterior spine, 

 with portions of two others on the left side. The left antero-lateral spine is 

 essentially entire, the representation being to make room for the separate 

 spine on that side. The postero-lateral spine is, by error, represented as 

 smooth in some of the figures. 



Fig. 6 b. The central spine of a larger individual, showing the slightly curved form and 

 spiniforous character above, while it is nearly smooth towards the base : the 

 latter feature is not always characteristic. 



Fio. 94. 



former and one in the latter, 

 with the brachial plates. The 

 opposite side of the specimen is 

 too much crushed to determine 

 satisfactorily the structure. 



Geological formation and locality. In the Keokuk limestone near War- 

 saw, Illinois. 



