78 E. Billings on the structure of the Crinoidea, ete. 
pond with the decreasing aperture, the Sane would be a 
deeply folded, flask-shaped sack, with a small round orifice 
like fig. 7, which is the internal gill of a pre r. 
In Policies tenuiradiatus, a species very characteristic 
of the Chazy limestone, the whole surface (in the condition in 
which the fossil is usually found) is covered with deeply striated 
thombs, the fissures being deepest where they cross the suture 
and growing gradually shallower as they approach the center of 
the plates, where they die out altogether. Detached plates oc- 
cur in vast abundance but no perfect specimens have ever been 
found. I discovered, however, several fragments of the body 
sufficient to give the general form and to show that, when the 
- surface is perfect, all these fissures are completely covered over 
by a very thin shell, and that, when they cross the suture there 
is a small pore in the bottom of each which penetrates to the 
interior. The rhombs of this species are thus external hydro- 
chylaqeous fluid eee outward ae the pores and filled 
the tubes, to be erated through the thin external covering by 
the aierouadins water. In Caryocrinus the water passed in- 
ery through the pores, into the tubes and erated the fluid 
in the general cavity of the body. 
The discovery that the fissures and pores of the Cystidea, do 
not communicate directly with the general cavity of the body 
is entirely due to Mr. Rofe. After reading his highly impor- 
tant paper, I re-examined a great number of specimens and 
found sufficient to confirm his observations. 
3. On the genus Codaster. 
Every author who has described a sapere oo this genus ~ 
remarked the peculiar striated areas in the rradial space 
Prof. McCoy, the founder of the genus, paiited out their re- 
semblance to the hydrospires of the Cystidea, but it was Mr. 
Rofe who first showed that they were also identical in struc- 
ture therewith. On comparing one of those with that of the 
cystidean Pleurocystites, fig. 5, we at once Patras that they 
are the same in the sricenal form while Mr. Rofe’s figures show 
that the section at d; d, has the structure of fig. 9, which only 
differs from fig. 5 6, in ‘being straight above instead of con- 
cave, and in being divided into two parts. This division is 
the result of the position of the arm which cuts the dap 
spire in two, in a direction parallel to the fissures. By 
ing the points d, a, and a, d, together we get figure 10, which 
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