. Annual report of the Regents. New York State Museum; Science. 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 \yz showing the fiv
. Annual report of the Regents. New York State Museum; Science. 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 \yz 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 ug. 9) posed to have seven rays, (A. septem- brachiatus; Cincinnatian) and Miller and Gurley one with but four (A. legrandensis; Kinderhook). Young specimens of A. a 11 e g a n i u s, A. b u 11 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 eganio s they reach the margin, but in the young of A. hamiltonensis and A. b u 11 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 ray
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