1886.] NATURAL SCIENCES OF PHILADELPHIA. 121 



The only known species is : 



1880. Hybocystites problematicus Wetherby, Cincin. Joum. Nat. Hist. (July). 

 P. Herb. Carpenter, 1882, Quart. Journ. Gcol. Soc. London (Aug.). Trenton 

 gr. Mercer Co., Ky. 



Family XVIII. HETEROCEINIDJE Zittel. 

 (Emend. W. and Sp.) 



Zittel and S. A. Miller included among tlie Heterocrinidse the 

 genera GrapMocrimis and Erisocrinns, which both have iinder- 

 basals, and which differ essentially in the plates of the azygous 

 side. We place in this family only Heterocrinus, locrinus and 

 our new arenera Stenocrinus and Ohiocrinus. 



The Heterocrinidae differ from the Cyathocrinidae and Poterio- 

 crinidae in the absence of underbasals, in the arm structure, and 

 the arrangement of their azygous plates. 



In 1866, Hall thought he observed in Heterocrinus two rings 

 of five pieces beneath the radials, and he adopted the term basals 

 for those of the proximal ring, and that of subradials for those 

 of the succeeding one. Afterwards, it was proved by Meek, Ohio 

 Paleont., i, p. 2, that the so-called " basals " proximal ring 

 were not plates of the calj'x but parts of the column. He de- 

 scribed the stem to be divided longitudinally, and the so-called 

 " basals," which in their vertical range were said to correspond 

 with the five segments of the column, as constituting the imper- 

 fectly developed uppermost stem joint. Meek proposed for these 

 plates the name " subbasals," and called those of the next ring 

 basals, while we used on Pt. I of the Revision the terms under- 

 basals and basals, respectively, as we took all of them to be 

 integral parts of the calyx. 



We have lately given this subject careful consideration, and 

 found by grinding the column in various species, that important 

 differences exist among the species originally referred to this 

 genus. We found that most of them have a pentapartite column, 

 of which the five sections alternate with the basals without form- 

 ing a part of the calyx, but that the column of Heterocrinus 

 simplex^ Hall's typical species, is tripartite, composed of three 

 equal sections. 



We have elsewhere shown that whenever the column is divided, 

 its sections alternate with the proximal ring of plates in the 

 calyx. They are placed interradially when those plates are under- 



