372 EF. B. Meek—Fossils of the Illinois Geological Report. 
central point in advance of it; precisely as the ambulacra in 
Comatula converge to the mouth in front of the anal opening, 
over by minute fixed pieces, as in the more complete Cyatho- 
erinites, fig. 13; the ambulacral canals in both cases passing 
under the vault-pieces, inward to the central opening. 
n the Blastoidea, there are, however, other small lateral 
openings in the summit, as seen at 7r, ‘7, in figures 2a and 26, 
and ats, s,in figure 5 of plate rx. These are the so-called 
ovarian apertures of many authors, and have been called hy- 
drospires by Mr. Billings, who, with several others, regards them 
a curious series of internal parts with which they con- 
nect, as the water-breathing organs of the animal. Although 
some recent investigations of the anatomy of existing crinoids, 
by Metschenhoff,* would seem to cast doubts on the correct- 
Prof. McChesney, in describing certain species of this group. 
These are small pore-like openings, very regularly dispos 
with relation to the interradial and other spaces around at the 
connection of the body and vault; one being placed near one 
side a the base of certain arms, at regular intervals, all 
aroun 
* Bull. Acad. St. Petersburg, XV, p. 508. 
my 
