1879.] NATURAL SCIENCES OF PHILADELPHIA. 331 



sive collections, into six divisions, for which we propose distinct 

 names. In doing so, however, we wish to have it understood that 

 we scarcely deem the characters upon which they are based suffi- 

 ciently important even for subgeneric separation. Still better dis- 

 tinctions may be discovered hereafter, and in the mean time this 

 arrangement will prove very convenient for comparative stud}'. 



The genus Poteriocrinus, of which there are now over a hundred 

 species known and described, was thought by Miller to be repre- 

 sented altogether by two, and of these the material at his com- 

 mand was very limited and imperfect, so that probably in order 

 to make the most of what he had to render his descriptions as 

 perfect as possible and to prove some of his theories more effectu- 

 ally he in some cases reconstructed the specimens from frag- 

 mentary pieces, which he supposed to be parts of the same species, 

 but which, as we now know, belonged, at least in some instances, 

 to different genera. The fact that Miller's figures cannot be re- 

 lied upon, and that his best original specimens can nowhere be 

 found (Austin), has produced continual trouble. Some of his 

 species have been badly defined by subsequent writers. This is 

 evidently the case with his typical species P. crassus. It is true 

 Miller's figures are not so intelligible as might be wished, yet 

 they prove plainly that the plates of the calyx in that species are 

 thin, with elevations radiating from a point near the centre of the 

 plates and meeting at the sutures those from adjoining plates. 

 Such costse as these elevations have often been called are found 

 very prominent in several species of Poteriocrinus from the Bur- 

 lington limestone, and in these they are not mere external mark- 

 ings, but are produced by a flexure of the plate itself. That the 

 structure was similar in P. crassus is plainly indicated by Fig. 7 Gr, 

 which represents folds on the inner surface of a radial not inter- 

 costal, as Miller makes it. In the figures of de Koninck's so-called 

 P. crassus, the plates, on the contrary, are massive, without plica- 

 tions, the surface simply granulose, and the articulating scar, 

 which in Miller's specimens scarcely fills one-third the width of 

 the radials, extends almost the entire breadth of the plate. Strange 

 as it may appear, it seems as if de Koninck took the plications 

 which in Miller's principal figures somewhat indistinctly resemble 

 the parasitic excrescences of one of his own specimens to be the 

 work of parasites ; and in no other way can we account for his 

 supposing such distinct forms to belong to the same species. The 



