Hambach — Revision of the Blastoideae. 23 



Pentremites roemeri, Shumard, is referred to the Chemuno- 

 group. 



"Looking at other characters than those of general form, 

 the specimens before me scarcely warrant the union of all 

 these species under the genus N^ucleocriniis or Elaeacrinus. 

 In jSTucleocrinus elegans, and allied forms, we have three small 

 basal plates and five short radials, which embrace the base of 

 the pseudambulacral fields; while the interradial plates are 

 extremely large, extending nearly the whole length of the 

 pseudambulacral areas. The anal side is often, or usually, 

 flattened, a little broader than the others, and is marked by a 

 narrow lanceolate plate, which extends from the opening to 

 the summitof the radial plates, resting upon them; thus, as it 

 were, dividing the interradial plate, leaving a narrow portion 

 on each side adjacent to the pseudambulacral fields. The 

 central area at the summit, between the ovarian openings, is 

 occupied by several small plates, which, in JVucleocrinus ele- 

 gans, converge to the center. 



' ' In the structure of the body, the typical forms of this 

 genus differ from Pentremites m the shoYi radial plates and 

 extremely elongated interradials, which fill nearly all the 

 space between the pseudambulacral areas; while the elongate 

 anal plate is a marked feature. Now when we compare 

 Pentremites norwoodi and Pentremites melo, we have 

 the same general form of body, with the extremely 

 elongate, instead of the short, radial or forked plates 

 which embrace the pseudambulacral fields ; and a small inter- 

 radial at the summit. The ovarian apertures, as well as per- 

 haps the central opening, sometimes preserve minute plates, 

 which close these orifices. The form alone can scarcely be 

 of generic importance; for, although the base of JSfucleocrinus 

 is usually concave, I have before me a species where the base 

 is not concave, and the three basal plates are quite prominent. 

 The only conspicuous difference between Pentremites nor- 

 woodi and Pent7^emites godoni and others of the latter form, 

 is in the depressed base and greater rotundity of the former 

 species, giving to it its similarity to Nucleocrinus. The Pen- 

 tremites norwoodi and Pentremites melo have not the anal 



