METAZOA ECHINODERMA. 155 



four species l of this genus were in reality different stages 

 of growth of one species, for which the older name of 

 Cyathocrinus iowensis is retained. After an examination 

 of a great number of specimens, it was found that the 

 young was represented by the species C. divaricatus Hall 

 which possessed good-sized basal plates. As the animal 

 grew older, these plates became smaller, while at the sa/ne 

 time the radials (subradials of Wachsmuth and Springer) 

 increased in size. This is seen in C. iowensis, which 

 these authorities have proved, is identical with C. rimi- 

 nalis Hall. The mature form, having the smallest basals 

 and largest radials, is C, malvaceus Hall. 



Poteriocrinus zeaeformis Schultze (No. 271; PI. 272, 

 figs, i, 2, P. circumtextus M. & G.), has a long slender 

 stem which is not seen in the figures. Its body is made 

 up of underbasal, basal, and radial plates with the first 

 arm sections or brachials fastened by suture to the 

 radials. 



The anal tube rises from the ventral disc, and is seen 

 in both the specimens (No. 271) and figures (PI. 272). 

 The long, delicate arms are forked and their pinnules can 

 be distinctly made out in the specimen (No. 271). 



Encrinus liliiformis Lam. (No. 273), is one of the best 

 known Crinoids. The body is so large that it needs 

 firmer support than the stem alone can furnish, and 

 therefore root-like extensions or cirri are thrown out 

 which help to fasten the animal securely in the mud. 

 The plates of the body are regular, consisting normally of 

 five underbasals, covered by the top stem joint, five 

 basals, and five radials. The oral plates are present in 

 the young but usually disappear in the adult, while the 

 anal plates are found only in the young. The anus per- 

 forates the oral disc within the circle of arms instead of 

 being outside the arms as in some Cystoids. 



1 Cyathocrinus iowensis O. & Sh., C. divaricatus Hall, C. malva- 

 ceus Hall, and C. viminalis Hall. 



