212 NEW YORK STATE MUSEUM 



There is usually a pore exactly at the corner of a plate with 

 three or four plates uniting to form its walls. The vertical 

 sutures also possess one or more pores besides those common 

 to both vertical and horizontal sutures. The corner pore and 

 the three which immediately surround it together occupy a 

 shallow basin formed by the thinner and depressed corners of 

 the joining plates. Such a basin is well shown at the left end of the 

 suture between plates a and b, figure 2. 



Nature of the pores in C. perforatus. In an aquarium speci- 

 men of Asterias forbesii under my observation, the papu- 

 lae average about 0.2 mm in diameter and, while the pores of C. p e r- 

 f o r a t u s are slightly smaller, they strongly suggest canals for the 

 extrusion of similar respiratory processes. These pores, and others 

 of like nature, will be hereafter called suturql canals. The position of 

 the larger and first formed sutural canals of C. perforatus, be- 

 tween brachia and on either side of the axial fold, is very suggestive 

 of connection with the water vascular system. If such was the case 

 the protruding respiratory processes might be considered as homol- 

 ogous with podia though not functioning as organs of locomotion. 

 How many of the arm plates lie below the horizon of the tegmen 

 in this genus is not known, but the permanently closed condition of 

 the arm bases must have tended to make functionless (in a respir- 

 atory sense) the podia perhaps formerly possessed by this region. 

 This would rather strengthen the idea that these external processes 

 were developed to compensate for the loss of the others. A^ery 

 similar structures in Palaeocystites, to be discussed farther on, are 

 more suggestive of papulae or external extensions of the coelomic 

 cavity, and as the arms of crinoids carry extensions of this cavity 

 one could with equal propriety maintain that the structures in ques- 

 tion were simply papulae such as we find on the aboral surface of 

 asteroids. It becomes desirable then to have a term which we may 

 use to designate all forms of exothecal or epithecal respiratory pro- 

 cesses regardless of the character of the subthecal cavities into 

 which they may open and though the term branchial vesicles has 

 been used as synonomous with papulae, we shall take the liberty of 

 using it here in the broader sense given above. As the use of the 

 term will be frequent we shall abbreviate it to b.v. or b.vs. It 

 seems fairly reasonable to hold, at least temporarily, that the sutural 

 canals of C. perforatus were occupied by b.vs. and that these 

 were sensitive and protected by possessing the power of rapid with- 

 drawal. Cliocrinus would thus become an example of the first 

 direction of b.v. protection outlined on page 202. 



