1886.] NATURAL SCIENCES OF PHILADELPHIA, 137 



and Cyathocrinidae, resembling the former in the absence of 

 underbasals and in the arm-structure, the Cyathocrinidae in the 

 arrangement of plates at the azygous side and of the ventral 

 tube. As the most characteristic features we mention the 

 extremely small visceral cavity, in which the genus resembles 

 Apiocrinus of the Neocrinoidea ; the comparatively large size of 

 the basals ; the absence of underbasals ; the position of the 

 azygous plate in line with the five radials; the large porous 

 ventral tube, and the condition of the pinnules, which are given 

 off regularly at certain intervals, not alternately from every joint. 



Belemnocrinus was referred by White to the Cyathocrinidae, 

 and he described the calyx to be composed of three rings of 

 plates. We have shown in 187T that the part which he took to 

 be the " basals " is the upper stem-joint, and that the dorsal cup 

 consists of only two rings of plates. We further directed atten- 

 tion to the affinities between Belemnocrinus and the recent genus 

 Rhizocrinus, which had been pointed out also by Pourtales, in 

 the Memoirs of the Museum of Comp. Zoology, vol. iv, No. 9, 

 p. 29. The construction of the dorsal cup in the two genera is 

 very similar, however, in Bhizocrinus, the sutures between the 

 basals are fused together; while in Belemnocrinus they are 

 plainly visible, and the former has no anal plate and no ventral sac. 



Belemnocrinus was placed by Zittel among the Poteriocrinidas, 

 although it has neither the arm structure nor the pinnules of that 

 family, nor the azygous plate, and not even underbasals. 



The name Belemnocrinus was used in 1876 by Munier-Chalmes 

 (Jour. Conch., Ser. 3, vol. xvi, p. 102) for certain basal plates, 

 evidently of a Blastoid, and changed by Oehlert to Belocrinus, 

 1882 (Extr. du Bull. Soc. Geol. de France, Ser, 3, p. 362). 



BELEMNOCRINUS White. 

 (PI. 5, figs. 10 and 11.) 



1862. White, Proc. Bost. Soc. Nat. Hist., vol. ix, p. 14. 

 1866. Meek and Worthen, Proc. Acad. Nat. Sci. Phila., p. 251. 

 1868. Meek and Worthen, Geol. Rep. Illinois, iii, p. 463. 

 1877. W. and Sp., Amer. Jour. Sci. (April), p. 253. 

 1879. Zittel, Handbuch der Palseont., i, p. 362. 



(Not Belemnocrinus Mun.-Chalmes =^ Belocrinus Oehlert.) 



Generic Diagnosis. Dorsal cup small, narrow, sometimes 

 almost tubular. 

 10 



