109 
PALEONTOLOGY OF NEW-YORK. 
Genus Homocrinus. 
Palaeontology of New-York, Vol. ii, p. 185. 
The differences indicated between this genus and Poteriocrinus are 
constant in all the Silurian species examined; while the general habits 
of the animals, form of body, etc. are in all respects similar to the 
carboniferous forms of Poteriocrinus. 
The generic description of the latter genus, having been framed for 
the Carboniferous species, would require a modifiation of the terms to 
include the Silurian species which I have indicated by the name of Ho¬ 
mocrinus, and which appear sufficiently distinct to constitute a separate 
genus. In the present state of our knowledge, there is about the same 
degree of difference between the species of Homocrinus and those of Po¬ 
teriocrinus, as exists between some species of the latter genus and those 
of Cyathocrinus. 
Ilomocrinns scop^mis (n. s.\ 
Plate I. Fig. 1. 
Body elongate-conical, subpentagonal above ; base comparatively large. 
Surface granulate or granulate-striate. Basal plates five, pentagonal, 
longer than wide, cuneiform above. Sub radial or costal plates longer 
than wide, three hexagonal, the other two heptagonal, truncate above, 
and supporting on the upper lateral margins a small intercalated qua¬ 
drangular anal plate. First radial or scapular plates five, pentagonal, 
wider than long; four resting upon the iqiper lateral margins of the 
contiguous subradial plates ; the fifth resting upon the subradial plate 
on one side, and upon the intercalated anal plate on the other : its 
vertical side adjoins the second anal plate, and the upper lefthand angle 
is truncated by the third anal plate, giving it an irregular hexagonal 
form with one extremely short side. The succeeding radial plates, to 
the number of three or four below the first bifurcating plate, are qua¬ 
drangular : first bifurcations equilateral. 
