82 £. Billings on tie structure of the Crinoidea, etc. 
inward about three lines, the main body being about one line 
from the lancet plate. There are five folds, each two lines 
deep ; and thus, if the thin shelly membrane, which consti- 
tutes the wall of the hydrospire, were spread out, it would 
have a width of 22 lines,—and the ten together would form 
a riband, about 18 inches in length, and nearly two inches 
wide. The object of the folding is, of course, to confine 
this large amount of surface to a small space, an arrangement 
which at once proves the function to be respiratory. Of those 
figured by Mr. Rofe, P. ellipticus Sowerby appears to have 
only one fold, P. inflatus, id., shows eight folds in one, and 
Another specimen figur Mr. Rofe under the name of 
ealis Say, has ie folds situated at a distance from the 
see dation of the lancet ogee as in P. obesus, From the 
rm of the organ [ think that Mr. Rofe’s specimen cannot be 
a species called P. florealis by Say. 
If it be granted that these organs are respiratory in their 
function, then, their five apertures should be called spiracles, 
—not “ovarian orifices.” The large anterior aperture would 
thus be the oro-anal spiracle. Applying this system of 
terminology to other groups,—the so-called ovarian orifice of 
the Cystidea, the homologous oo of Nucleocrinus, Co- 
daster, Granatocrinus and of the Paleozoic Crinoidea oe 
rally (but not of the recent forms) , Should be styled the or 
anal orifice. 
I think that the side of an Echinoderm in which the mouth 
is situated should be called “anterior” even although the anus 
and the mouth be confluent in one orifice. Most starfishes 
have but one aperture for mouth and vent and yet it is called 
the mouth by naturalists generally. Why not call the under- 
side of a star-fish “the anal or posterior side,” and the cen- 
tral oe the “‘ anus ?” 
Dr. B. F. Shumard has shown (Trans. Acad. Nat. Sci. St. 
ae. vol. J, p. 243, pl. 9, fig. 4,) that in perfect ——— 
all, the six summit apertures are closed b 
ec, Ba plates. Ina specimen of the same sestura se 
me by Mr. Lyon, in which those plates are partly preserved, I 
find that there is a small pore in each of the five alee of the 
aperture. The five ambulacral grooves enter the inte- 
cen r 
rior through these pores. I have copied his figure but modi- — 
fied it by adding the pores, fig. 15. He also found that the — 
summit of P, sulcatus, Roemer, was covered with an integu- 
ment of small plates arrang in the form of a pyramid. From 
these facts he infers that in all the pentremites the summit 
ore will = found in perfect specimens, to be closed in 4 
similar man 
SEES Ver fee Sa en ee er ye ae tee, ea mS See 
