544 



GEOLOGICAL SURVEY OF IOWA. 



Dr. TROOST remarks, " If the number of plates which com- 

 " pose the body of an encrinite determine its genus, then 

 " the one under consideration must perhaps be placed in that 

 " of CYATHOCRINITES ; but if the arrangement of these plates 

 " is also necessary to determine its genus, then this crinoid 

 " cannot belong to the Cyathocrinites, and forms a new genus, 

 " to which I have applied the name of Zeacrinites"*. 



GENUS ZEACRINUS (TROOST). 



BASAL plates five, usually small and hidden by the column. 

 Subradial plates five, pentagonal or hexagonal, rarely with 

 six subradials : first radial plates five, pentagonal ; second 

 radials five, of the same form as the first, relatively reversed, 

 with one or two more in the anterior ray ; interradial plates 

 none : anal plates four, six or more. Summit unknown. 



FIG. 64. 



The accompanying diagram (fig. 64), 

 of the original specimen of Dr. TROOST, 

 will illustrate in part the characters 

 above given. The basal plates are hid- 

 den by the column in the deep cavity 

 of the base. The subradials are ex- 

 tremely narrow and elongated, their 

 length indicating very nearly the depth 

 of the cavity of the base. The first ra- 

 dial plates are much elongated, nar- 

 rowed and pointed below, and very 

 wide upon their upper margins. The 

 second radials are short and broad, an 

 intermediate one coming in on the an- 

 terior rayf. 



* I have transcribed these observations, as well as the specific description of this spe- 

 cies, from the MS. of Dr. TKOOST'S memoir upon the Crinoideae, which is to be published 

 in the Smithsonian Contributions to Knowledge ; having been permitted to make such 

 references and citations as would enable me to verify any of the genera and species 

 which I might describe in the Iowa Report. By this means, although Dr. TROOST'S paper 

 has not yet been published, he has the precedence which belongs to him. 



t The following is the description of Z. -magnoliceformis as given by Dr. TROOST : 



" Elongated, cylindrical. Pelvis small pentagonal? divided? This supposed pelvis lies 



