CONTRIBUTIONS TO PALEONTOLOGY. 145 



for the original of Troost's Genus Olivanites ; recognizing the 

 specific name verneuili, given by Dr. Troost. 



I conceive that there can be no doubt as to the propriety of 

 restoring the earliest name ; and I have therefore adopted Mr. 

 Conrad's name of Nucleocrinus. 



Regarding only the general form of these bodies, this genus would 

 include several species, heretofore described under Pentremites, 

 from the Carboniferous limestones of the Western States, viz : Pen- 

 tremites norwoodij Owen and Shumard; P. meloj Owen & Shumard; 

 P. curtus, Shumard, and others; while the Pentremites {Olivanites) 

 verneuili = Elaacrinus verneuilij Rcemer, and Olivanites angularis, 

 Lyon, are of the age of the Upper Helderberg limestones; and the 

 JVucleocri7ius elega7is, Conrad, and at least one other species, occur 

 in the Hamilton group. The Pentremites rcRmeri^ Shumard, is refer- 

 red to the Chemung group. 



Looking at other characters than those of general form, the spe- 

 cimens before me scarcely warrant the union of all these species 

 under the Genus Nucleocrinus or El^acrinus. In JYucleocrinus 

 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 t;.e summit of 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 JV. elegans, converge to the centre. 



In the structure of the body, the typical forms of this genus differ 

 from Pentremites in the short radial plates and extremely elongated 

 interradials, which fill nearly all the space between the pseudambu- 

 lacral areas; while the elongate anal plate is a marked feature. Now 

 when we com^arePeiitremites norwoodi and P. 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 interradial at the summit. The ovarian apertures, 

 as well as perhaps 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 Nucleocrinus is 

 usually concave, I have before me a species where the base is not 



[ Senate, No. 116.] 19 



