352 PROCEEDINGS OF TIIE ACADEMY OP [1885. 



the projecting faces of the interradials at the dorsal side. There 

 are five interaxillary plates of a similar form, supported by the 

 dorsal interaxillaries, and ten small triangular interbrachial pieces, 

 interposed in such a manner between the foregoing plates that 

 always an interradial and an interaxillary meet laterally above 

 an interbrachial. The second and third rings consist of four 

 plates each; the fourth of ten. The two former ones together 

 form the neck-like prolongation of the body, and the plates of the 

 fourth ring, combined with those of the first ring, the partition 

 walls encasing the arms. 



The interradials and interaxillaries of the first ring are uniform 

 in size and shape ; they are knife-like, their blunt sides exposed 

 to view, their sharp edges turned inward. Toward the lower end 

 where the plates decrease in depth, lateral flanges project out 

 from their inner edges, which unite suturally, and enclose the 

 visceral cavity, while the knife-like outer portions, as we under- 

 stand it, are merely extraordinary protuberances, like the nodes 

 or spines in some Actinocrinidae, but forming by means of their 

 connected wing-like extensions a cover or protection for the 

 arms. 



The plates of the second ring fit into the ten angles formed by 

 the preceding plates, but do not alternate with them. Two of 

 them are a little wider, and these are alternately arranged with 

 the smaller ones. The two narrower plates are generally longer, 

 angular above, while the two others are truncate, and their lateral 

 faces slightly sloping upward. When united, they form a funnel 

 with the narrow opening upward. Transversely they form a ring 

 with ten protuberances, which on their outer surface represent 

 longitudinal ridges. The ridges correspond in position with the 

 interradial and interaxillary partition walls which overlap them, 

 while the alternate grooves form the inner angle of the niches. 



The third ring, like the second, consists of four plates, but 

 these, as a rule, are not so large, and have a more irregular 

 arrangement ; two of them are generally shorter, and do not 

 touch those of the preceding ring. They are provided at their 

 outer faces with ten longitudinal ridges, which, to their full 

 length, are overlapped by the partition walls, which extend down- 

 ward from the fourth ring of plates. 



The plates of the fourth ring are constructed upon a similar 

 plan as those of the first ring. Like those, they consist of ten 



