186 NEW YORK STATE MUSEUM 



preparation of this account the authors were relying mainly on 

 the original specimen of Agel. kaskaskiensis Hall, which 

 belonged to the Worthen collection. That Ech. optatus 

 W. & M. is not the same thing as A. kaskaskiensis has 

 not been proven, and every indication favors the presumption 

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

 facts, viz, that in the description of Echinodiseus and E. o p - 

 tatus, the remotest reference to A. kaskaskiensis is 

 avoided, and also that in the edition of Miller's North American 

 geology and paleontology (1889) next succeeding the date of 

 Worthen and Miller's publication, A. k a s k a s k i e n s i s is 

 referred to Echinodiscus. The basis of the genus Echinodiscus 

 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 1 another species of this 

 genus, E. samp so ni, 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 imperfect and a third likewise 

 imperfect but affording some important details. 



The specimen for which F. Roomer proposed the name 

 Haplocystiteis (H. r hen an a, 1851) has recently been figured 

 by Jaekel (Stammesgeschichte 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 smooth as in E c h i n . 

 s a m p s o n i and A . k a s k a s k i e n s i s but as the specimen 



1 Geol. sur. Ind. 17th an. rep't. 1891. p. 76, pi. 12, fig. 16. 



