54 EE. Billings on the structure of the Crinoidea, ete. 
it is quite certain that that system was at first, (or in the undevel- 
oped stage in which it existed in the Cystidea,) destitute of the 
cesophageal ring. . 4 
Tn Codaster a further concentration of the respiratory organs is — 
exhibited. There are here only five hydrospires and they are 
all confined to the circle around the apex. ‘T'wo of them are 
incomplete in order to make room for the large mouth and vent 
m v, fig. 2.) They are each divided into two halves by an arm, 
al, a2, &e. ey are only connected with the arms to this ex- 
tent, that these latter lie back upon them. The arms are pro- 
that in the former the arms are erect and do not touch the hy- 
pires, whereas in the latter they are reeumbent and lie back 
Soke of the two genera are perfectl homologous organs. 
If we grind off the test of a species of the facta genus, selecting 
one for the Uaey eet which has broad petaloid ambulacra such as 
those of P. S i 
the two in each interradial space, being so connected, at their 
er angles, that their internal cavities open out to the exterior 
ough a single orifice or spiracle (s, f s. 8 and 4). This is 
Shown in fig. 4, intended to represent the structure of P. 
cus (Sowerby) as deseribed by Mr. Rofe, Geol. Mag., vol 
