122 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
throughout, by means of which the surrounding water is brought in direct 
contact with any part of the body. 
There are good reasons for believing that in the Camerata the water for 
respiration was introduced near the arm bases through small openings, de- 
scribed by us as respiratory pores, and then followed the canals and passages 
along the test. Such openings have been observed not only among the Actino- 
crinide and Batocrinidx, but also among the Melocrinidz and Rhodocrinide. 
In the genus Dolatocrinus, they are large and slit-like as in Ophiurids, in Bato- 
crinus and Actinocrinus round, and in Gilbertsocrinus at the outer end of long 
tubes. The openings are always located between the rays and their main 
divisions, a little above the arm regions. Some species of Dolatocrinus have 
from four to six to each interradius, and two to four to each interdistichal 
space, all arranged horizontally. In Dolatocrinus this vascular system prob- 
ably extended only over the peripheral portions of the disk, for the inner 
floor at the middle portion is perfectly smooth in the specimens. In Bato- 
crinus and Teleiocrinus it probably extended to the outer margins of the orals 
(Plate V. Figs. 16 and 17); while in Physetocrinus, when the orals are un- 
represented, it apparently occupied the whole tegmen. 
We now come to the ventral structure of Siphonocrinus. It will be 
remembered that in S. armosus not only the ambulacra, but large portions 
of the anal tube, are subtegminal, and that the latter lies across the mouth 
and covers portions of the ambulacra. The tube, however, in two other 
species of this genus opens out centrally, thus showing that the subtegminal 
condition of the tube had no important bearing upon the general structure 
of the disk. As we understand the case, the anal tube, which is actually 
the outer end of the hind gut, in place of becoming free and piercing the 
central part of the disk as in the other two species, was roofed over in 
S. armosus by the interambulacral pieces in a somewhat similar manner to 
the calyx ambulacra of Megistocrinus. 
Now if it is true that in forms like Physetocrinus, Batocrinus, Actinocrinus, 
and Siphonocrinus, there is no second integument, it may be considered as 
proved that a “vault,” as an independent structure, did not exist in any of 
the Camerata, nor, in fact, in any of the other groups, and that the structure 
to which the term has been applied in these forms was evolved phylogenet- 
ically from the disk of the primitive types, of probably Pre-Silurian time. 
The disk of the Fistulata also experienced notable changes in its paleon- 
tological development, but these took place on different lines. The plates 
