76  £. Billings on the structure of the Crinoidea, etc. 
In order to avoid the, use of double terms, I propose to call 
— = hydrospires,” and their aa “pores,” “fissures,” 
r “ spiracles” according to thei 
Caryocrinus ornatus the (hess oF (fig. 4,) are of a 
rhomboidal form, and have each of the four sides bordered by 
a single row of small tubercles. Some of these tubercles have 
a single pore in the summit, while others are Lc Noli with 
a variable number,—from two to twenty, or perhaps more,— 
thus becoming vesicular or spongy. It is only the apex of the 
tubercle, however, that has this structure, for, when this is 
worn off, there is only a single pore to be seen. The pores 
penetrate through the plates pa do not communicate directly 
with the general pguated of the body. Internally each hydro- 
spire consists of a number of flat tubes arranged parallel to 
each other and itr side 1 side, in the direction of the dot- 
ted lines in fig. 4, a. tube receives two of the pores 
seen on the exterior—one oon at each end. These tubes are 
represents the tubes, 
pecimens of OC. ornatus almost entirely empty are often 
found and in some of these the internal form of the hydro- 
bg es is sometimes preserved. Those that I have seen "have 
e form of small rhomboidal pyramids, with four slightly 
convex sloping faces, and composed of a number of vertical 
parallel p eothic casts of fhe interior of the tubes—the 
substance of the tube itself not being preserved. I have, how- 
ever, several soto transverse sections, in which I think the 
thin walls can be see 
by 
ies rnrouge the ex caseedtagtyt thin membranous sell, "that 
composed the walls of the ra The number of pores ‘varies 
with the size of the individual. In large specimens these are 
from 800 to 1000. 
a ea 
3 
" 
