186 NEW YORK STATE MUSEUM 



piepai-atioD of this account the authors were relying mainly on 

 the original sjiecinien ofAgel. kaskaskiensis Hall, which 

 belonged to the Worthen collection. That Ec4i. optatus 

 W. & M. is not the same thing as A. k a e k a s k i e n s i s has 

 not been proven, and every indication favors the presumption 

 that it is. Side light is thrown on this proposition by two 

 facts, viz, thai in the description of Echinodiscus and E. op- 

 tatus, the remotest reference to A. kaskaskiensis is 

 avoided, and also that in the edition of Miller's Noi'th Amerioa/n 

 geology and paleoutologg (1889) next succeeding the date of 

 Worthen and Miller's publication, A. kaskaskiensis is 

 referred to Echinodiscus. The basis of the genus Echinodiscue 

 was laid mainly on the constitution of its interradial plating, 

 which is not imbricating but mosaic, on the mode of departure of 

 the ambulacra from the oral aperture and the narrowness of the 

 rays, but nothing is said concerning the direction of the rays. 



Mr Miller subsequently described^ another species of this 

 genus, E. sampsoni, from the Keokuk group at Boonville 

 Mo., a highly incomplete fragment of the oral surface, which 

 nevertheless shows narrow, undulating ridgelike rays and a 

 mosaic of polygonal interradial plates. Except for its larger 

 size there is little to distinguish it from A. kaskaskiensis. 



So far then it appears that a quite distinct type of structure 

 among the agelacrinites has been founded on specimens one of 

 which was fairly complete but incorrectly described, a second 

 audaciously fragmentary and imjjerfect and a third likewise 

 imperfect but atfording some important details. 



The specimen fur which F. Koemer proposed the name 

 Haplocystites (H. r he nan a, 1851) has recently been figured 

 by Jaekel iStanimesgeschichte der Pelmatozoen. 1899. pi. 3, 

 fig. 3). This is an internal oast showing two rays and part of a 

 third. These are quite narrow and have the general aspect of 

 those of Agelacrinites while the plates are polygonal and 

 mosaic. The surfaces of these plates are ©mooth as in Ech in . 

 sampsoni and A. kaskaskiensis but as the specimen 



» Oeol. 8ur ltu\. 17th an. rep't. 1891. p. 76, pi. 12, ttg. 16. 



