ISST).] NATURAL SCIENCES OF PHILADELPHIA. 129 



I. HETEROCRINUS Hall (not Frass). 

 (Restricted and redefined by W. and Sp.) 



1879. Revision Palseocr., Pt. i, p. 68. 



1880. Wetherby, Cincin. Journ. Nat. Hist , July number. 



1881. Wetherby, ibid., April number. 



EeterocrinuSj as defined by Hall and revised by Meek, contains 

 so widely different species that a subdivision becomes necessary. 

 This has been conceded by previous writers. Wetherby, in 

 describing his H. Milleri, expressed the opinion that in the com- 

 parative size of the column, and in the plates of the calyx, that 

 species differed sufficient!}' from Heterocrinus simplex to be sep- 

 arated at least subgenerically. And a year later, he directed 

 attention to his E. Vaupeli, which he thought to be very distinct 

 in the structure of its arms. H. Vaupeli, if it is a good species, 

 which we doubt, agrees in its arms and pinnules closely with H. 

 constrictus and IT. laxus, with either of which it may be identical, 

 but not with H. simplex, as suggested by S. A. Miller. The 

 species heretofore referred to Heterocrinus vary in the composi- 

 tion of their radials, in the structure of arms and pinnules, and 

 in the column. Heterocrinus simplex, Hall's type, has five basals 

 of varying form, owing to irregularities in the radials. The 

 radials in two of the rays consist of a large single plate, two 

 others are divided into two sections, and the fifth one rests upon 

 the azygous plate, which agrees in size with the lower half of 

 the compound radials. The compound i^lates consist of two 

 pieces each, which together, agree closel}- in form and size with 

 the two single plates. The brachials are large ; they consist of 

 two nearly equal plates, united by syzj^gy, and support ten heavy, 

 simple arms. The arms, to their full length, are composed of 

 syzygial joints, which, as we think, were connected by suture and 

 not by articulation. The epizygal or pinnule-bearing pieces are 

 slightly wedge-shaped, and alternate with one another; the lower 

 or h3'pozygal ones rhomboidal, and their upper and lower sides 

 are parallel. Pinnules stout and comparatively long. 



All other species heretofore referred to this genus, with the 

 exception of ^. canadensis, which may be identical with H. sim- 

 plex, have a somewhat different arm structure. Not only are the 

 pinnules given off at greater intervals, but they attain the size 

 and form of arms or armlets, which sometimes branch again, and 

 extend to the general height of the primary arms. The latter 

 agree also in having a stricth' pentagonal and pentapartite 



