190 NEW YORK STATE MUSEUM 



or all contrasolar, as in A. dicksoni Billings (Trenton). 

 Four rays contrasolar and one solar is the usual expression, 

 as shown by A. ( L e p idodiscus) 

 s q u a m o s u s Meek and A. ( E c h i - 

 n o d i s c u s ) k a s k a s k i e n s i s Hall 

 of the Keokuk and Chester groups 

 of the lower Carbonic, A. c i n - 

 c i n n a t i e n s i s Roemer, A. hoi- 

 brooki and A. p i 1 e u s Hall of the 

 Cincinnatian group. In A. hamilton- 

 ensis Vanux. (middle Devonie) two are fig. 3 a. dicksoni Binings 



x \y z showing the five contra- 

 SOlar and three COntraSOlar. Even the solar rays and the ambulacral 



plates which were regarded as 



number of the rays seems not to be always perforate by Binings (From 



. Ottawa field nat. club. Trans. 



five, as Paber has described a species sup- 2. issi. piate u g . 9) 

 posed to have seven rays, (A. s eptem- 



brachiatus; Cincinnatian) and Miller and Gurley one with 

 but four (A. legrand e n s i s ; Kinderhook). 



Young specimens of A. a 1 1 e g a n i u s, A. b u 1 1 s i and of the 

 A. hamiltonensis show that the ambulacral rays in early 

 growth extended in direct radial lines to the margin or elevated 

 submarginal wall. They did not however pass on to the aboral sur- 

 face, though in A. all e ganio s they reach the margin, but in 

 the young of A. hamiltonensis and A. b u 1 1 s i these rays 

 abut directly against a highly developed ridge. The final course 

 of the rays is then not determined except with the approach of 

 mature conditions, but is nevertheless constant, and we have no 

 record of any departure from the regularity and uniformity of 

 their direction in a given species or homogeneous group of 

 species. 



This feature is notably one in which specific character is not 

 expressed or suggested before the commencement of mature 

 growth, and it seems therein to lose all value as a feature of 

 higher (generic) distinction, though persistent as a specific 

 character. The primitive direction of these rays is repeated in 

 the adult expressions of the earlier agelacrinites, as cited above. 



Size, length and structure. Among the Agelacrinitidae (re- 



