4 



In describing the Poteriocrinidce I shall not use the subgenerie 

 terms hitherto proposed by various authors, for the following rea- 

 sons : First, I see no beneficial result that is likely to come from 

 cumbering the nomenclature of paleontology with such terms, and 

 secondly, because any proposed subgenerie formula that groups to- 

 gether such diverse forms as Zeacrinus mantformis, Yandell & 

 Shumard, and Poteriocrlnus Bissclli, Worthen, can be of no practical 

 advantage in the study of this group of crinoids, and hence, until 

 some satisfactory generic characters can be pointed out, by which 

 they may be separated, it seems advisable to include them all under 

 the generic name originally proposed by Miller for them. 



All the new species described in the following pages will be fully 

 illustrated in the 7th Vol. of the Geol. Surv. of Illinois, now in 

 course of preparation. 



POTEEIOCRINUS COXANUS. N. SP. 



Body above the medium size, obconic, gradually swelling from 

 a truncated base to the summit of the radial plates, where it is about 

 one-fourth wider than high. Basal plates as wide, or a little wider, 

 than high, forming by themselves a low pentagonal cup, about twice 

 as wide as high. One subradial on the anterior side is longer than 

 wide, the others about as wide as long, all pentagonal, there being 

 but two distinct angles on their lower margins. 



Radials nearly once and a half as wide as high on the anterior 

 rays, curving in on their lateral borders so as to give a pentalobate 

 character to the upper part of the body. 



Brachials two, the hrst quadrangular, and the second pentan- 

 gular, and both more than twice as wide as long, the second support- 

 ing on their sloping sides the first divisions of the rays. Only two 

 of the rays and a part of the third, are to be seen, the others l)eing 

 concealed in the rock. In one of these, probably the anterior ray, a 

 second bifurcation takes place on the fifth plate in each division, and 

 the outer branch is seen to divide once more about the tenth plate, 

 and the inner division on the twenty-fourth to the twenty-sixth plate, 

 beyond which the arms of this ray are not preserved. 



On the right antero-lateral ray the second bifurcation takes 

 place on the fourth plate in each division, the outer branch dividing 

 twice more on the eighth and twenty- second plate, and the inner one 

 twice on the twenty-fourth to the twenty-sixth plate, beyond which 

 they are not preserved. This gives twelve visible arms to this ray, 

 and it is quite possible there were other divisions beyond, as the arms 

 extended about two inches beyond the last divisions that are pre- 

 served. The arms are stout, and composed of rounded, short, nearly 

 parallel plates, that give off delicate pinnules from their inner mar- 

 gins. The upper part of the ventral tube is exposed by the partial 

 removal of the arras, showing that this organ was trumpet shaped, 

 and crowned with heavy hexagonal plates, produced at the center 

 into rather sharp nodes, while below, the plates are thinner, and 

 crossed by about three sharp ridges, that are most prominent in the 



