E. Billings on the structure of Crinoidea, Cystidea, etc. 231 
_ There is also evidence of the existence of minute marginal 
plates on ” side of the groove. 
The hydrospires are ten elongated sacks, 
each with two deep folds. They are per- 
ce homoge with those of Pentre- 
oe differing therefrom in not be- 
a tee in pairs; consequently there are 
ten spiracles instead of five. The mouth, 
or oro-anal orifice, is larger in proportion 
to the size of the bo dy than it is in Pen- 
tiirotigh’s reer e section tremites, Mr. Meck informs me that the 
gil the, bydrospires preserved. mouth in some of the Blastoidea is pro- 
tyarongieer ge" cacne of the tected by a single vale age ek it 
wu like the lid of a jug. m the structure 
of the one Tam ig to think that in Mi ais it pos- 
cen : 
hil., vol. viii, p. 380, 1. Sg fig. 17). His fi represents the 
fossil with the apex ae Ww ard » r. Fe . 3 
eh a to ie both mouth and vent, which accords with my 
lew. (Mon. der Hieueiik p. 878). In 1868 I discovered 
the five small pores at the apical extremities of the ambulacral 
re our., I, xevii, p. 353, and Annals Nat. Hist., 
V, vol. 4, p. 76). In ade it : difficult to see these pores, 
but if a silicified specimen, which has been fossilized in a cal- 
careous matrix, be aod: a an acid for two or three minutes, 
the acid cleans them out and they then become distinctly visible. 
I believe these to be the pores ugh which the ovarian tubes 
cles, five ovarian orifices, ‘and one oro-anal foertare, ere 
are no true radial P lates. The whole of the test with the ex- 
ception, perhaps, of the ambulacra belongs to the perisomatic 
