142 PROCEEDINGS OF THE ACADEMY OF 



its prominent horn-like interradial pieces, and its strongly carinated radial 

 plates. These carinse are so prominent and regular, as to give the body 

 the appearance of being divided into ten sharply angular ridges, or lobes, 

 extending from near the summit to the base, the intervening depressions at 

 the sutures, and those containing the pseudo-ambulacral fields being about 

 equal. 

 Locality and position. Dry Fork, Brown Co., Ills. St. Louis Limestone. 



Pentkemites melo, var. projectus. This Pentremite agrees with P. melo of 

 Owen and Shumard, excepting that its base is proportionally a little larger, 

 and instead of being concave, projects so as to be distinctly visible in a side 

 view. Its pseudo-ambulacral areas are also not continued down quite so near 

 the base of the radial pieces as in P. melo. It may be a distinct species, but 

 the difference seems to be scarcely of specific importance. 



Both of these forms differ from the typical species of the genus Pentremites, 

 in having each pair of ovarian openings distinctly separated, instead of closely 

 united with merely a thin septum between. In this character, as well as in 

 form, and the prolongation of the pseudo-ambulacral areas, they agree with 

 the genus Nucleocrinusot Conrad, (=Eleacrinus, Roemer,) from which they dif- 

 fer in having the anal and oral openings distinct as in the true Pentremites. 

 They constitute a sub-genus of Pentremites, occupying a position between the 

 typical forms of that genus and Nucleocrinus. 



Locality and position. Burlington, Iowa. Burlington Limestone. Collec- 

 tion of Mr. Charles Wachsmuth. 



ASTERWEA. 



Genus Petkaster, Billings, 1858. 



Petraster Wilberanus. This beautiful star-fish resembles rather closely 

 Petraster rigidus of Billings, (Decade III. Org. Rem. Canada, plate ix. fig. 3*,) 

 but is smaller, and has more slender rays, with more angular spaces between. 

 It also differs in having but two ranges of plates on each side of the ambula- 

 cral grooves, on the under side, instead of three. These pieces are about of 

 the same size in each row, and sometimes appear to alternate ; they are all 

 rather prominent, and those of the outer range project a little laterally in the 

 form of small nodes. Towards the outer extremities of the rays, however, 

 the lateral ranges are contracted behind the others, so as to be scarcely visi- 

 ble from below. About 23 of these pieces may be counted on each side of the 

 ambulacral furrow in each ray. The ambulacral furrows are very narrow, 

 and indeed seem to be closed towards the extremities of the rays, by the gra- 

 dual approximation of the inner rows of pieces on each side, which alternate 

 and appear to fit together. 



Our specimen only shows the under side, but along the outer margins of 

 two of the rays, there is some appearance either of the overlapping of some of 

 the dorsal parts by pressure, or of a slightly developed disk. This part does 

 not seem to have any distinct range of marginal plates, but appears to be made 

 up of small pieces, covered with granules, or bases of small spines. 



We take pleasure in dedicating this interesting species to Prof. C. D.Wilber, 

 of the Illinois State Normal School, to whom we are indebted for the use of 

 the only specimen we have seen. 



Greatest diameter about 1 inch ; smaller diameter 0*33 inch. 



Locality and position. Oswego, Kendall Co., 111., in rocks of the age of the 

 Trenton or Hudson River Group of the N. Y. series. 



MOLLUSCA. 

 BRACHIOPODA. 



Genus PRODUCTUS, Sowerby, 1812. 

 Productus magncs. Shell large, semi-oval, or sub-hemispherical in outline ; 



[JuDe 



