1881.] NATURAL SCIENCES OF PHILADELPHIA. 335 



Basals three, short, with a tripartite rim formed by the projec- 

 tion of the lower margin of the plates. Primary raclials 3x5, 

 of nearl}^ similar form but decreasing in size upward. The third 

 radial gives off 1 X 10 secondary radials, and these form the two 

 main trunks, of which each one gives off, alternately throughout 

 all the bifurcations, and from every first joint, an axillary, and 

 to the opposite side a fixed arm plate, the one supporting the 

 next order of radials, the other being succeeded by additional 

 arm plates, which on becoming free, pass into a simple arm. 



Interradials numerous, from five to seven or more, the second 

 resting between the second and third primar}^ radials, the upper 

 ones being in contact with the interradial plates. The space between 

 the rays is wide, deeply depressed, especially at the posterior 

 side, and this depression extends to the vault. Anal area very 

 wide, the first plate in line with the first radials, and of their 

 size. There are two plates in the second range, three or four 

 in the third, with a large number of small pieces above, which 

 imperceptibl}' connect with the plates of the vault. 



Interaxillary plates one to three. Yault depressed its radial 

 portions formed into ridges or lobes, which rapidly increase in 

 prominence toward the arm regions. It is composed of moder- 

 ately small, apparently irregularly arranged pieces, which are 

 more or less spiniferous. 



Anus excentric, probably in form of a simple opening through 

 the vault. Arms unknown. 



Geological Position^ etc — Gennseocrinus is restricted to the 

 Hamilton group of America.. 



We place here the following species : — 



*1S62. Gennaeoorinris calypso Hall. (Actinocr. calypso) 15th Rep. N. York, St. 



Cah. Nat. Hist., p. 133. Hamilton gr. Western N. Y. 

 »1861. Gennaeoor Cassedayi Lyon, (Actinocr. Cassedayi) Proc. Acad. Nat. Sci., 



Phila., p. 410, PI. 4, figs. 3, 3a. Encrinal limesit. Near Lousville, Ky. 

 *1862. Gennseocr. caulioulus Hall. (Actinocr. cauliculus) loth Rep. N. York. 



St. Cab. Nat. Hist., p. 132. Hamilton gr. Western N. York. 

 *1862. Gennseocr. eucharis Hall. (Actinocr. eucharis) 15th Rep. N. York, St. 



Cab. Nat. Hist., p. 130. Hamilton gr. AVestern N. York. 

 *I860. Gennseocr. Kentuckiensis Shumard. Type of the genus. (Actinocr Ken- 



tuckiensis) Am. Journ. Sci. and Arts. (ser. 2), vol. 28, Septbr. ISoi), p. 238, 



Cat. Pal. Foss., p. 345. Lower part of Hamilton gr. Beargrass Quarries, 



near Louisville, Ky. 

 Syn. Actinocr. cornigerns Lyon & Cass., 1859. (not Hall, 1858). 

 *1862. Gennaeoor. nyssa Hall. (Actinocr. nyssa). 15th Rep. N. York. St. Cab. 



Nat. Hist., p. 129. Hamilton gr. Western N. York. 



