E. Billings on the structure of the Crinoidea, ete. 77 
It has been stated by some authors that the pores were pas- 
sages for the protrusion of internal organs connected with the 
vitality of the animal. The fact, however, that the pores do 
not penetrate into the general cavity of the body, disproves 
this theory ; and, moreover, through many of the tubercles— 
those with a vesicular and spongy summit, such protrusion 
am be utterly impossible. 
In pind oA ornatus there are thirty hydrospires ar- 
ranged as follow 
- 1. Tenat the bysesSadaal of each on a basal plate and the 
_ other half on one of the subradials, their longer diagonal ver- 
tical. 
2, A zone of six around the fossil at the mid-height—their 
_ longer diagonals horizontal. These seem to be imperfectly 
developed, for, on the inside, the tubes occupy only a small 
_ space in the center. 
| 3. A third band of fourteen—two of them with their iy 
_ diagonals vertical and the others arranged in six pairs, 
_ diagonals of each pair inclining toward each other, el 
- at an angle of about 30°. There are only three interradii in 
Caryocrinus : the mouth is placed in one of them — the two 
form as fig. 5a, i. e the form of a rhomb, longitudinally 
_ striated at right angles to the suture, and with no pores. The 
__ transverse section in Plewrocystites only differs from that in 
_ internal gill with a single spiracle. The surface is not flat, as 
it is in many species, but concave as shown in the section ; 
at the same time, but not diminishing the superficial extent 
of the walls of the folds although altering the form to corres- 
