66 PROCEEDINGS OF THE ACADExMY OF [1886. 



other Articulata in the position of the interradials and may prove 

 to be the type of a distinct family. 



F. Roemer established the family Anthocrinidae to receive 

 Anthocrinus and Crotalocrinus, and Pictet, as Dnjardin and 

 Hup^, recognized the family Anthocrinidffi, but referred to it only 

 Anthocrinus. As Anthocrinus proves to be a synon3"m, the 

 family name will fall with it, and we shall distinguish the family 

 as Crotalocrinidae, and follow Zittel in referring to it Crotalo- 

 crinus, Enallocrinus, but not Gleiocrinus. 



The Crotalocrinidae are distinguished by the possession of a 

 ventral tube or anal appendage, located ventrally near the per- 

 iphery. In Crotalocrinus it consists of a tube composed of eight 

 A^ertical rows of heavy quadrangular pieces. In Enallocrinus its 

 form is unknown. The famil}^ differs from the Ichthyocrinidse 

 in a similar way as Platycrinidae from Actinocrinidie in that the 

 higher radials are imperfectly developed. 



The Articulata, therefore, fall into two families, which are 

 defined as follows : 



A. IcHTHYOCRiNiDiE. Basc dicyclic. Underbasals unequal, 

 proportionally very small, rarely visible externally. Basals gene- 

 rally small. Dorsal cup chiefly built up of radial plates of differ- 

 ent orders, abutting laterally against each other or separated by 

 interradials. Number of radials variable in genera, species and 

 individuals. Radial and arm plates decreasing in size in the suc- 

 cessive orders, each division being about half as wide as the 

 preceding one, and of uniform size in corresponding divisions of 

 the ray, but the plates of adjacent raj'^s generally alternate with 

 each other. The line of articulation between radials and arm 

 plates is frequently undulating, and there are sometimes additional 

 patelloid pieces. Arms uniserial, bifurcating, generally touching 

 laterall}^ so as to form a wall continuous with the calyx. Arm 

 plates with straight sides and very deep ambulacral grooves. 

 Pinnules apparently wanting. 



Interradial system chiefly developed on the ventral side. Spe- 

 cial anal plate sometimes resting on the basals, sometimes upon 

 the radials, and sometimes wanting dorsally. Anus unknown in 

 most of the genera. The radials are united longitudinally by 

 articulation, laterally b}^ ligament, the interradials among each 

 other and with the radials by a loose suture, admitting of motion 

 and producting flexibility in the calyx and vault. 



