218 TJie American Geologist. October, 1895 
concave. Underbasals, ii ])resent, liitldeii beneath the upper 
stem joint. Basals Ave, four of them being equal with acute 
angles above, the fifth truncate above. Primary" radials three, 
— four in one ray of one example, — by rive of unequal size, 
wider than long.' Three of the first radials are heptagonal, 
while two are hexagonal. Secondary radials three in number. 
Two arms spring from the bifurcating plate of each secondary 
sei'ies of radials, making twenty free arms in all. Arms short 
and rather heavy, made up of single joints folded in or over- 
lapping at the top. Short, strong pinules, apparently along 
the entire length of the arms but more crowded toward the 
ends. No so-called patelloid plates present in any of the 
specimens. A single, large, nine-sided interradial to each 
space except the azygous area. (The type specimen of A. 
concavus, instead of a single plate, has apparently some mi- 
nute accompanying lateral plates which may really be frac- 
tui-ed parts of the large plate.) The anal or azygous area is 
filled by three irregular plates accompanied by one or two 
smaller ones to the right and above. No appearance of an 
anal tube or proboscis. A single small, rounded, axillary 
plate rests between the first and second radial plates of the 
secondary series. Column moderately large, round and com- 
posed of even thin joints. Central perforation rather small. 
This fossil occurs in the Hamilton beds of Callaway Co., Mo. 
Type, Arisfocrinus tuntcavus (Rowley). The type specimen 
was first described b}^ the author in the American Geologist* 
under the name Ta.i-ocrinus concavus. Afterward other fea- 
tures were brought to light by the use of the knife, and in the 
same journalf other illustrations followed and the near rela- 
tion of this crinoid to Onychocriaiis was pointed out. Further 
study has led to the belief that it does not naturally belong to 
any known genus, and we have accordingly created a new 
generic term for its reception. It is evidently close to Ta.ro- 
crinv.s, from which it diifers in the shape of the calyx, the en- 
tire absence of the minute plates above the interradials and 
the possession of pinulte, ditfering in this latter respect from 
all known ichthyocrinoids. In general outline Arisfrocrinus 
diifers much from Onychocriint.s, but, in the possession of pin- 
*Vol. XII, p. 304, Nov., 189.3. 
tVol. XIII, p. 153, March, 18&4. 
