1879.] NATURAL SCIENCES OF PHILADELPHIA. 291 



nated as "free radiaU," but for which we have adopted the term 

 " brachials," consists of one to two or more by five plates on which 

 the arms originate. 



Arras simple or branching, comparatively long; either provided 

 with rather strong pinnulse, alternately arranged, or, in the ab- 

 sence of these, the ambulacral groove is covered with two rows 

 of alternating pieces, more or less wedge-shaped, sometimes 

 strongly cuneiform, and interlocking. 



There are from one to four anal plates within the calyx. When 

 there is a single anal, the symmetry of the body is generally bila- 

 teral, but, in case of two or more, the form is irregular, because 

 the plates tend obliquely toward the right side of the body. The 

 anal plates support a ventral sac, which is cylindrical, convoluted, 

 club- or balloon-shaped, and which occasionally attains immense 

 proportions. The sac is bordered with rows of pores or fissures; 

 its upper extremity closed, so far as observed ; the anal opening 

 lateral. Interradial plates proper entirely wanting. 



Calyx surmounted by five large oral plates, with a central 

 opening between them, and forming at their sutures five shallow 

 ambulacral grooves converging toward the centre. Central open- 

 ing covered by the apical dome plates, and the five grooves arched 

 over by two rows of small immovable pieces, alternately arranged. 



Column round or pentagonal. 



The Cyathocrinidae differ from the Ichthyocrinidse in having a 

 solid inflexible vault, built up of oral plates; in possessing but a 

 single radial to each ray; and in the absence of interradial plates. 



1. HETEROCRINE Hall. 

 (Diagram PL 16, Fig. 2.) 



1843.'lall. Geol. Rep. New York, vol. i. p. 278. 

 1859. Billings. Geol. Surv. Canada, Decade IV. p. 48. 



1865. Meek and Worthen. Proc. Acad. Nat. Sci. Phila., p. 147. 



1866. Hall. 24th Rep. N. Y. State Cab. Nat. Hist,, p. 210. 

 1873. Meek. Geol. Surv. Ohio. Palreont., vol. i. p. 2. 



The genus Heterocrinus varies from the typical Cyathocrinidae 

 in several important particulars : first, in the apparent absence of 

 underbasals in some of the species ; second, in certain irregulari- 

 ties in the radial plates. In the former respect it agrees with 

 Hi/bocrinus and Anomalocrinus, in the latter with Dendrocrinus. 



The irregularities in the radial parts seem at first sight to be 



