296 PROCEEDINGS OF THE ACADEMY OP [1879. 



pound plates, those that are divided by horizontal sutures, occur 

 in similar rays as in Heterocrinus, being always found in the right 

 posterior and either in the left lateral, or in the anterior ray. The 

 radials of the remaining ra3 r s are either simple or bisected verti- 

 cally, the two halves taken together being similar in form to the 

 simple plates. The lower segment of the former compound plates 

 is subquadrangular, the upper one axillary and pentagonal, its 

 lower edge slightly concave to fit the convexity of the abutting 

 margin below. The ra} T s with simple radials have generally fewer 

 brachials than those with compound plates, and this gives to the 

 Crinoid that abnormal, irregular appearance which is the most 

 characteristic feature of the genus. 



Arms divergent at their origin ; long, slender, bifurcating irregu- 

 larly several times above, the divisions being often of unequal 

 size; rounded, and composed each of a single range of pieces. 

 Pinnulse strong. First anal plate resting transversely between 

 the upper sloping sides of the posterior radials ; succeeding plates 

 smaller and longitudinally arranged. 



Column stout, round, composed of very thin discs or segments, 

 and having near the base a large pentagonal opening. The seg- 

 ments have the appearance of being composed of numerous little 

 anchylosed spicula of irregular size and form (Meek). 



Anomalocrinus has its closest affinities with Heterocrinus, to 

 which it was referred in 1865 by Meek and Worthen as a subgenus. 

 Not so apparent are its relations to Hybocrinus, with which the 

 same authors afterwards similarly combined it. It certainly dif- 

 fers from them both very distinctly in the shallow and depressed 

 form of the body, in the form and arrangement of the radial 

 plates, and in the arms. 



Geological position. Lower Silurian, so far as known. 



Two species have been described : 



1869. Anomalocrinus caponiformis Lyon. (Ataxocrinus caponiformis), Trans. 



Am. Pbilos. Soc, vol. xiii. p. 464, pi. 27, figs. 0, 01, 02,03. Hudson River 



Gr. Cincinnati, Ohio, and Kentucky. 

 1865. Anomalocr. incurvus Meek & Worth. (Heterocrinus t (Anomalocr.) in- 



curvus), Proc. Acad. Nat. Sci. Phil., p. 148, 1868, Meek & Worth. 



Hybocrinus? (Anomalocr.) incurvus, Geol, Rep. 111., vol. iii. p. 327, pi 4, 



fig. 3 a, b. Hudson River Gr. Cincinnati, 0. The latter is probably a 



new species. 



