312 PROCEEDINGS OF THE ACADEMY OF [1885. 



etc., must be considered simply as an ornamentation of the calyx. 

 They represent, as stated by Carpenter, " a character of alto- 

 gether minor importance as compared with the morphological 

 difference between the lateral union and the isolation of the 

 radiate." 



In Part II we have placed under Actinocrinidae all Crinoids 

 without underbasals, in which the interradial plates are connect- 

 ed by suture, and the basals support the radials, and frequently 

 a large anal plate, but none of the regular interradials. This ex- 

 cluded the allied genus Acrocrinus, in which basals and radials 

 are separated by a large number of accessory pieces. We ex- 

 cepted also the Galyptocrinidae with Eucalyptocrinus and Calli- 

 crinus, which differ essentialby in their vault structure, and the 

 Barrandeocrinidse for other reasons to be explained hereafter. 



The Actinocrinidse, as they were defined b}^ us, comprise a well- 

 defined natural group ; and we find it difficult to subdivide them, 

 unless it be upon the presence or absence of an anal plate in line 

 with the first radials, i. e., the bilateral symmetry of the one group 

 as contrasted with the more or less pentamerous symmetry in the 

 other. In making this division, we place the Stelidiocrinites and 

 Melocrinites with their almost regular sj-mmetry in the one 

 group, and the Agaricocrinites, Periechocrinites, Actinocrinites 

 and Batocrinites in the other, the former as Melocrinidas, the lat- 

 ter as Actinocrinidae. 



Etoemer, Lethaea Geogn., 1855 (Ausg. 3), p. 228, distinguished 

 Melocrinidae from Actinocrinidse, the latter on account of their 

 larger azygous interradius, and having three in place of four 

 basals. Zittel partly recognized these groups, but added to the 

 Melocrinidse Scyphocrinus Zenker (not Hall), Corymbocrinus and 

 Abacocrinus, the hitter with an anal plate upon the basals, thus 

 proving that he made the number of basals the distinctive char- 

 acter. He divided our Actinocrinidae into the families Briaro- 

 crinidee, Carpocrinidae, Dinner oci'inidse, Actinoc?'inidee and Poly- 

 peltidae. 



Our Platynicridae were subdivided into Plat3 r crinites and Hex- 

 acrinites, the one with strictly pentamerous symmetry in the 

 calyx, the other bilateral. The two groups are easily recognized, 

 and will be continued., but ranked as families. 



The Platycrinidse have been described by us and other writers 

 as having a single interradial plate in contact with the radials. 



