FOSSIL CRINOIDS. 127 



other genera. Prof. E. J. Chapman, of Toronto, in 1882 undertook to make 

 this the basis of a general classification of the Crinoids; but it is unavailable 

 among the fossils, owing to the uncertainty of the facts in so many forms. 



Another fact to be noted is the frequent presence in these genera with very 

 ponderous arms, of a short first primibrach, often very much shorter than any 

 succeeding ones. This is very marked in Schultzicrinus, and also in Cupresso- 

 crinus and Petalocrinus. 



The mutual relations of the genera composing this group may be expressed 

 as follows: — 



Analysis of the Genera. 



Dicyclic ; base undivided ; radials perforate. 

 Anal opening lateral through dorsal cup 



Central axial canal, with 3, 4, or 5 peripherals. 



Arms branching more than once Arachnocrinus. 



Arm simple, abutting, with long brachials Schultzia-inus. 



Arms unknown, probably simple, divergent, and 



with short brachials Gasterocoma. 



Only 4 arm-bearing radials Nanocrinus. 



" 3 " " " Scoliocrinus. 



Axial canal simple, without peripherals Achradocrinus. 



Anal opening not through dorsal cup 



Central axial canal, with 3 or 4 peripherals Myrlillocrinus. 



Arachnocrinus Meek and Worthen. 



1866. Geol. Surv. Illinois, II, 177. 



1879. Wachsmuth and Springer, Rev. Pal., I, 92. 



1896. Zittel-Eastman, Text-book Pal., 156. 



1900. Bather, Lankester's Treatise on Zool., Ill, 175. 



This genus has never been well illustrated. Hall's figures of Cyathocrinus 

 bulbosus being the only ones published, and they entirely failed to show the 

 most important characters of the calyx. The two species described by Wach- 

 smuth and Springer have never been figured at all, save for one non-instructive 

 specimen by Rowley in Greene (Contr. Ind. Pal. XVIII, PI. LIV, fig. 1). Having 

 the type specimens, and nearly all the others that have been found at the Falls 

 of the Ohio, I am in position to illustrate these species intelligibly; and some 

 newly discovered material, in addition to such of the types as can be found, 

 makes the same possible for the New York species. These are all that are 



