72  &£. Billings on the structure of the Orinoidea, etc. 
through the substance of the plates, and nly penetrate down- 
ward into the interior at the central space (¢ 
—is a plan of the summit of the widely known and 
remarkable fossil Caryocrinus ieee (Say). In this ne 
cies there are only three, instead of five, groups of arms. 
large individuals there are from pas to twenty free arms 
(but always arranged in the three groups) with a small pore at 
the base of each. This pore is about the size of the ovarian 
pore of an Echinus and can only be seen in well preserved and 
clean specimens. The ambulacral grooves have not yet been 
observed but their course is meats by three low rounded 
ridges, which may be seen, in e specimens, —— from 
a large heptagonal ae sabilted at (c). The mouth (mv) is 
valvular, composed of from five to eight or ten “pistes, and 18 
always _ pay near the margin between the two anterior 
groups of arms. With the exception of the ambulacral pores 
there is ipoeitively no other aperture in the summit of Cary 
erinus. If it be true that the mouth of an Hchinoderm 
must be always situated in the radial center, then Caryocrinus 
and also nearly all the paleozoic genera were destitute of that 
aperture. 
Caryocrinus is a genus which seems to form a connecting 
link between the Crinoidea and the Cystidea. By examining 
numerous well polished — I find that the structure of the 
respiratory areas is the same (in general plan) as that of the 
genera Glyptocystites, Plouroeytite and Echinoencrinites, as 
will be shown further o e arms are also arranged in three 
groups as in Spher malt and Hemicosmites, while the mouth 
is valvular. On the other hand, the long cylindrical column 
and the arrangement of the arms around the margin, with the 
ambulacral pores at their bases, are crinoidal characters 
In addition to the above, the following species may be re- 
ferred _ as examples of Crinoids with the mouth separate 
from the center of the radial system. 
eo tesselatus (Phillips).—Figured by J. Rofe, 
eol. Mag., vol. ii, p. 8, £3. The figure represents a cast 
of the interior of the vault showing the five ambulacral grooves 
in relief. The mouth is situated in the angle between the two 
anterior grooves 
Strotocrinus perumbrosus (Hall, sp.).—Figured by Meek 
and Worthen in the Geology of Tlinois, vol. ii, p. 188, f. 5. 
The specimen is 13 lines in diameter, the ambulacral center 
13 lines from the anterior margin, and the mouth 11 lines.* 
* In taxi last I received from Messrs. Meek and Worthen a paper entitled, 
‘- Notes on some points in the structure and habits of the Paleozoic Crinoidea. 
Of all che papers relating to this subject yet published on this continent, this one, 
