HISTOEICAL. 17 



B. Stylida, Crinoids with a jointed column. 



a. The tegmen formed of a skin. 



Pentacrinidse, Apiocrinidee, Eugeniacrinidae, Encrinidae, Cupressocrinidse, Cya- 

 thocrinidse. 



b. The ventral surface covered by heavy plates^ immovably united. 



Poteriocrinidse, Rhodocrinidsej Platycrinidae, Actinocrinidae, Melocrinidae, 

 Ctenocrinidse, Sagenocrinidae, Anthocrinidae. 

 C. The arms imperfectly developed. 



Haplocrinidae and Gastrocomidae. 



Roemer's families are natural groupSj except his Cyathocrinidas, among 

 which he united a number of widely different forms. But this is partly due 

 to Miller, who had included with Cijathocrinus forms which were afterwards 

 referred even to different orders. Roemer, believing that Miller's typical 

 species, Cyathocrinus planus was a Poteriocrimis, made his second species 

 Oyathocrinus tuber culatics, which PhilHps in 1843 had made the type of 

 Taxocrinus, the type of Cyathocrinus. 



Together with the Classification was published Roemer's classical memoir 

 on the Cystidea and Blastoidea, of which especially that of the latter fur- 

 nished most valuable additions to our knowledge of the morphology of that 

 group. 



In 1845 appeared the Memoir of Leopold von Buch on the Cystidea. He 

 gives excellent descriptions of several genera, and places the group at equal 

 rank with the Blastoidea and Crinoidea. 



De Koninck and Le Hon, in 1853,^ described a number of new species 

 from the mountain limestone of Belgium, and proposed certain changes in 

 the terminology of the calyx plates. The proximal ring of plates he calls 

 " basals," whether the species is monocyclic or dicyclic ; those of the second 

 ring in dicyclic forms "" sous-radiales." The radials comprise all plates up to 

 the first axillary; and the succeeding plates of the rays, when parts of the 

 calyx, are '^articles brachiaux," otherwise arm plates. The term "inter- 

 radiales " is applied only to the plates of the four regular sides ; those of 

 the posterior side are " pieces anales." 



Another classification was brought out by Pictet, in 1857,t who "divided 

 the Crinoids into nine families. The first and ninth of his families contain 

 almost exclusively Neozoic forms. The former embraces the Comatulce and 

 Marsupites, to which was added the Palseozoic Ast^locrinus {Agasskocrinus) ; 



* E,ecl)erches sur les Crinoides du Terrain Carbonifere de la Belgique. 

 t Traite de Paleontologie, par F. J. Pictet, Paris, 1857, Tom. V., pp. 278-345. 



3 



