130 PROCEEDINGS OP THE ACADEMY Of [1886. 



column, contrary to H. simplex^ in which the column is stouter, 

 almost circular, and regularly tripartite. The species with a 

 quinque-partite column are divisible again into two groups, the 

 one with a straight, comparatively small ventral tube, the other in 

 which the tube is thread-like, convoluted, and even in its coiled 

 state extending beyond the limits of the arms. We hold these 

 differences important enough to malvc them the basis for another 

 separation, proposing for the latter the genus OhiociHnus, with 

 H. laxus Hall = Ohiocrinus laxus as type, and for the other 

 the genus Stenocrinus with H. heterodachjlus JisiW ^= Stenocrinus 

 heterodactylus as type. 



Heterocrinus inaequalis and H. arficulosus Billings have been 

 referred by us to Calceocrinus ; H. crassiis and sitbcrassus 

 to locrinus. 



The genus Heterocrinus thus restricted may be defined as 

 follows : 



Revised Diagnosis. Calyx small ; subcylindrical ; tapering but 

 slightl}' from the column upwards. 



Basals five, more or less unequal, without underbasals ; the so- 

 called subbasals of Meek representing the upper stem joint. 



Radials very irregular, and varying among the rays in number 

 as well as in size. There are two segments in the two antero- 

 lateral rays, while the three remaining rays have but one, this, 

 however, nearly as large as the two in the other rays. The two 

 plates at the right postero-lateral side consist of the az3gous 

 piece the lower one and of the radial, which upon its upper 

 side supports the brachials, giving off laterally a small ventral 

 tube. Arms ten, composed of single joints, alternately united bv 

 syz3^gy, with strong pinnules from every second joint. 



Column tripartite, almost circular ; axial canal large, pentalo- 

 bate, the lobes directed interradially. 



Locality.^ Position^ etc. Trenton and Hudson River group of 

 America, 



1859. Heterocrinus canadensis Billings, Geol. Rep. Can., Decade iv, p. 48, PI. 4, 



fig. 5. -.-Trenton limest. Ottawa and Montreal, Canada. 

 184;i. H. simplex Hall, Geol. Repr. N. York,' vol. i, p. 280, PI. 76, figs. 2a-d; also 



Geol. Surv. Ohio, Paleont. i, p. 7, PI. 1, figs. 4 a-c, 5 a-b, 6 a-b. Hudson 



River gr, Cincinnati, Ohio. 

 *1S7;'. H. grandis Meek, described as H. simplex var. grandis, Geol. Surv. Ohio, 



Paleont. i, p. 9, PI. 1, fig. 6, and figured by Hall as H. simplex in the 24th 



Rep. N. Y. State Mus. Nat. Hist. PI. .3, fig. 11. Hudson River gr. 



Cincinnati, Ohio. H. grandis occurs at a higher horizon, is more robust and 



has shorter arm joints than H, simplex. 



