- 
. also the vent. The mouth does not lie where J. Miiller and — 
Volborth sought for it, viz: in the center of the ambulacral — 
ows ; and the organ, interpreted as the vent by Volborth — 
ded as an external sexual — 
74 E. Billings on the structure of Crinoidea, etc. 
of Crinoids whose external characters show that, in them, the 
mouth cannot be in the central point from which the grooves 
radiate, 
With respect to Prof. Thompson’s theory, I freely admit that 
if it is true that in all the echinodermata, fossil and recent, 
the mouth is the radial center, then, that aperture, must be 
the one which I call the ambulacral orifice in the Cystidea. The 
views, however, advocated by me in my Decade No. 3, appear 
to be gradually gaining ground. As these fossils are rare, few 
have occasion to study them, and consequently the subject has 
not been much discussed since 1858, the date of the publica- 
tion of that work. The following are the only authors, so far 
as I have ascertained, who have given their opinions on this 
is now quite certain ; in the last-named group it was, doubtless, 
and von Buch, is more correctly regar 
organ,” Geol. Mag., vol. v, p. 181, Dr. Liitken’s trans.] 
2. On the pectinated rhombs and calycine pores of the Cystidea. 
