232 Cincinnati Society of Natural History. 
pentagonal. Primary radials three by five. Regular interradials three. 
Azygous interradials about six or seven. Arms arising free from the 
third primary radials, and bifurcating at about the eighth or tenth 
plate after becoming free. Pinnules comparatively large and long. 
Surface very slightly ornamented. Vault moderately convex, and from 
appearances abutting upon the third primary radials, and extending 
up as a covering to the ambulacral grooves in the free arms. 
It occurs in the middle part of the Hudson River Group. 
\ 
PYCNOCRINUS GERMANUS (S. A. Miller). 
This was first described as Glyptocrinus shafferi var. germanus, but 
I now regard it as sufficiently distinct to bear a specific name. Calyx, 
small, saucer-shaped. Basals, minute. Primary radials three by 
five, wider than long. Regular interradials three, the two upper ones 
being very small. Arms ten, as they arise free from the third radial. 
They bifurcate at about the twelfth plate after becoming free. Arms 
and pinnules, coarse and strong. 
This species is distinguished from P. shafferi, by having a shorter 
calyx and much stronger and longer arms, which bifurcate at a greater 
distance from the calyx. The surface is without ornamentation. 
It occurs in the middle part of the Hudson River Group. 
The question may be asked, why should the presence of secondary 
radials be regarded as of generic importance, and not the presence of 
tertiary radials; or, in other words, if it is proper to found the genus 
Pycnocrinus, upon species having no secondary radials, why should 
we not have a genus limited to those having secondary radials asin G. 
dyeri, but not having any tertiary radials as G. decadactylus has? 
The answer is, because the tertiary radials are removed one step further 
from the stable part of the body toward the arms, where the bifurca- 
tions may not be uniform in different rays, and where the number of 
plates may differ, in different specimens, in the same species. There 
are greater variations, in the different species, in the region of the 
tertiary radials, than in the region of the secondaries. It would be a 
step from the region of greater stability to that of lesser stability, 
which is precisely the difference between a generic character and a 
‘specific one. All the species we have hud under consideration have 
primary radials, and almost invariably three by five, and all have 
secondary radials, but widely differing in number, except these two, 
and these seem, otherwise, to be distinct, in important characters, 
from all the others. If the secondary radials were as uniform in 
