192 NEW YORK STATE MUSEUM 



departinjr from each extremity and the fifth from the side. This 

 is a condition which is common to most true a^elacrinites, but 

 it is very much more pronounced in all postsihiric species, being 

 no doubt emphasized in expression by the more slender rays. 



Anal pyramid. The valved anal aperture may be situated 

 centrally o*r laterally in an i-nterradius. It is interesting to note 

 that, whenever a reversal is present among the rays, it invariably 

 affects that adjoining this aperture, so that the pyramid lies in 

 a subcircular interradius bounded by the concave curves of 

 neighboring rays, as though indeed the function of alimentation 

 were conserved by this close approach of the ambulacra. 



Mode of growth. These bodies divide themselves into species 

 which/ grew attached to other bodies and those which may have 

 rested on other surfaces and so have taken a flattened form but 

 were not permanently fixed. To the former, apparently, belong 

 all or nearly all of the earlier species as well as the Devonic 

 Agelacrinites hamiltoneneis, the supradevonic A. 

 butt si and A. legrandensis. So far as the evidence 

 goes, A. a 1 1 e g a n i u s, A. k a s k a s k i e n s i s ( A. o p t a t u s), 

 A. sampsoni, A. squamosus, A. beecheri, all late 

 species, were not attached, even in pretty early growth stages. 

 Thus^ while fixation continued throughout the history of the 

 group as a species character, freedom from fixation pertained 

 almost wholly to the latest representatives, save in cases where 

 notable degeneration had set in. Such permanently attached 

 species as pass beyond Devonic time are also marked by the per- 

 sistence of a primitive expression in other respects, in size, short- 

 ness and directness of arm, and breadth and composition of the 

 marginal border. 



Summary. It appears from the foregoing that we may leave 

 out of consideration as a generic character of the agelacrinites 

 the variation in the direction of the rays and may consider as 

 structures of convenient generic value 1) the character of the 

 thecal plates, whether a) squamous or b) mosaic, and if the latter, 

 whether 1) polygonal and smooth or, 2) irregular and sculj)tured; 

 2) the character of the rays, whether a) long and whiplash 



