374 PROCEEDINGS OF THE ACADEMY OF [1888. 



in the two forms, there cannot be the slightest doubt that they be- 

 long to the same group, and that that group is the Camarata. It 

 might indeed be fairly said that the calyx of Crotalocritius, in all 

 that determines its subordinal rank, is nothing more than a dicyclic 

 Marsupiocrinus. The mode of union of the plates in the dorsal cup 

 is also somewhat similar in the tw'O genera. There are in both of 

 them along the suture lines small conical pits, which penetrate a 

 short distance inward but do not pass through the test (PI. XIX, fig. 

 5) ; the inner half of the apposed faces is jjeculiarly striated, indicat- 

 ing a sort of syzygial union. On the other hand, the vast multipli- 

 cation of arms, with their lateral connection into a net-work, con- 

 stitutes a wide differentiation of this type from any other group of 

 the Camarata, and is without a parallel among crinoids generally. 

 But this is a character which does not affect the fundamental plan 

 of structure, which unites it unquestionably with the Camarata. 



Another very remarkable character of this fjimily is the perfora- 

 tion of the higher radials and arm joints by a dorsal or axial canal, 

 which in the higher radials is very large, ramifying to the arms, and 

 in Crotalocrinus extends to their extremities. The canals of each 

 ray unite into one on the inner surface of the first radials, and pass 

 downward toward the base. This perforation, and the fact that the 

 arm joints are united also by muscles instead of ligaments only, dis- 

 tinguishes the family sharply from all other Camarata. It was this 

 mainly that led us to place them among the Articulata not knowing 

 the solid structure of the vault. The arms in this group must 

 have possessed a higli degree of flexibility, being found sometimes 

 closely folded together lengthwise, often spread out horizontally — 

 even dropping over the calyx — and sometimes compactly inrolled 

 for a considerable distance from the ends, as shown in our figure (PI. 

 XIX, fig. la). 



There is one point in Crotalocrinus which is not clear to us, and 

 on which our specimens do not seem to throw much light. Johannes 

 Miiller^ gives the following description of the ventral structure of 

 the arms. " Dieser Canal [speaking of the ventral furrow along the 

 the arm joints] ist queriiber von kleinen Pliittchen verdeckt, welche 

 meist alternirend" in einander greifen. Zu den Seiten stehen auf der 

 Volarseite der Glieder, die Ambulacra einfassend, iiusserst zarte 

 Pinnulae oder schmale .Saumpliittchen, von denen mehrere (3-4) 

 auf die Liinge eines Gliedes kommen. Diese Pinnulae sind unge- 



1 Ueher den Ban der Echinod. Abh. Bed. Akad. d. Wissenscli. 1853, p. 189. 



