146 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



concave, and the three basal plates are quite prominent. The only 

 conspicuous difference between P. norwoodi and P. 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 

 P. norwoodi and P. melo have not the anal side conspicuously wider^ 

 more prominent, or flattened; which is the character observed in 

 all true Nucleocrini. 



The different arrangement of parts, also, in the two genera, causes 

 a different mode of increase in the plates, and a different surface- 

 character. 



There is likewise an intermediate form represented by the Gra- 

 NATOCRiNus of Troost { Peutremites granulatus[l] of Ecemer). This 

 species is elliptical in form, with depressed base embracing in the 

 bottom of the cavity the three small basal plates, while the radial 

 plates reach halfway up the sides of the body. The anal side is not 

 conspicuously different from the others, and the summit is unlike 

 Nucleocrinus; while it is more nearly like Pentremites norwoodi. 

 This species is strongly granulose or tuberculose. The Pentremites 

 sayi appears to me to belong to the same type : its base is not de- 

 pressed, leaving the three basal plates protruding; while the radial 

 plates reach about one- third the entire length, in this respect ap- 

 proaching Nucleocrinus. In both these species the plate on the anal 

 side occupies the entire space between the pseudambulacral fields, 

 presenting scarcely any important difference from the other inter- 

 ambulacral or interradial spaces. 



I would therefore suggest the separation of the species under the 

 name originally given by Dr. Troost, viz. Granatocrinus. 



The Genus Nucleocrinus of Conrad may be characterized as 

 follows : 



GENUS NUCLEOCRINUS (Conrad, as emended). /, . ) ^-^ 



General form of body elliptical or ovoid, supported on a slender 

 column. Basal plates three, minute. Radials five, small and not 

 deeply forked, receiving the bases of the narrow elongate pseud- 

 ambulacral fields. Interradial plates six, four of them elongate, 

 broadly lanceolate, truncate or concave on the lower side, and 

 occupying the space between the pseudambulacral areas : a nar- 

 row intercalated plate on the anal side reaches from the aperture 

 to the radial plate, dividing the interradial on that side into two 

 narrow curving plates. Oral aperture central; the summit occupied 

 by five or more plates. Ovarian apertures in five pairs at the 

 extremities of the pseudambulacral fields. Anal aperture lateral; 



