1879.] NATURAL SCIENCES OP PHILADELPHIA. 301 



both under Poteriocrinus. In 1861, however, he described two 

 new species under Homocrinus, from good specimens. They are 

 not Poteriocrinus, for they have no pinnuhe, nor Gyathocrinus, 

 for they have an extra intercalated plate above the basals ; nor 

 Dendrocrinus for that plate is not radial ; but their affinities are 

 the closest with the latter, with which they agree in all principal char- 

 acters. We therefore regard Homocrinus as a subgenus under 

 Dendrocrinus, and propose the following description, with Homo- 

 crinus scoparius Hall as type : 



General form and arrangement of plates like in the typical 

 Dendrocrinus, except at the posterior side where the lower por- 

 tion of the compound plate is pushed slightly to the rear, thereby 

 becoming a regular anal plate or support for the ventral sac. 

 Hence in Homocrinus only the upper portion of the compound 

 plate is a radial, and there are two anal plates, one subquad- 

 rangular, between the posterior radials, and supported on the 

 truncated basal; and a smaller one resting obliquely between two 

 basals, the right radial and the other anal plate. 



The underbasals are perhaps proportionally larger than in Den- 

 drocrinus. The arms have no pinnulae, and this, together with the 

 different arrangement of the anal plates forms the best distinction 

 from Poteriocrinus. The ventral sac is without mesial ridge or 

 lateral costse. Column, so far as observed, round. 



Geological position, etc. Upper Silurian in America. In 

 Europe it has been found in the Devonian. 



Six species are known : 



1852. ? Homocrinus cylindricus Hull. Geol. Rep. N. Y., vol. ii. p. 186, pi. 41, 

 figs. 2 a, b ; Hall, 1859, Poteriocr. cylindricus. Correct. List of N. Y. 

 Foss. Niagara Gr. Loekpnrt, N. Y. 



(The specimens are too imperfect for identification.) 



*1844. Homocr. fusiformis Roeuier. Rhein. Ueberganzsgeb., p. 61, pi. 3, fig. 2. 

 Schnur, Bactocrinitis fusiformis, Steininger's Geogr, Beschr. der Eifel, p. 

 38. Miiller, Poteriocrinus fusiformis, Neue Echin. d. Eifl. Kalk., p. 250, 

 pi. 2, fig. 2; also Schultze, Echinod. Eifl. Kalk., p. 45, pi. 5, fig. 1 a-g ; 

 Devonian. Eifel, Germany. 



*1868. Homocr. nanus Roemer. (Poteriocrinus nanus.) Paljeontographia, by 

 Wm. Dunker, p. 151, pi. 29, figs. 2, 3. Devonian. Bundenbach, Ger- 

 many. 



1852. Homocr. parvus Hall. Geol. Rep. N. Y., vol. ii. p. 185, pi. 41, figs. 1 a, b, c. 

 Poteriocrinus parvus Hall, 1859. Corr. List N. Y. Foss. Niagara limest. 

 Lockport, N. Y. 



(Probably a very young individual of some other species.) 



