1881.] NATURAL SCIENCES OF PHILADELPHIA. 355 



Pictet^ arranged Rhodocrinus^ AcanthociHnus^ Dimerocrinus, 

 and Thysanocrinus under the Cyathocriniens, Lijriocrinus and 

 Scyphocrinus Hall (not Zenker), under the Carpocriniens, and 

 all under the Cj'athocrinidje. 



Roemer,^ who was the first to propose the name Rhodocrinidae, 

 referred to it only the genus Bhodocrinus, placing Sagenocrinus 

 with the Sagenocrinidse, Thysanocrinus with the Poteriocrinidse, 

 and Dimerocrinus which we take to be identical with Thysano- 

 crinus he referred to the Cyathocrinidae. 



The great dissimilarity which manifests itself in these classifi- 

 cations, must be partly attributed to the imperfect knowledge 

 which prevailed with regard to some of those genera at that time. 

 It was evidently the intention of the writers to group the 

 Crinoids according to the presence or absence of underbasals, the 

 number of basals and the arm structure, but these parts had 

 been often incorrectly represented, or were as yet entirely unknown. 



A very marked improvement is visible in the classification of 

 ZitteP who placed among the Rhodocrinidae, Ollacr-inus, Bhodo- 

 crinus, Acanthocrinus, Bipidocrinus, and Thysanocrinus^ and 

 proposed the name Glyptocrinidae for Glyptocrinus , Glyptaster, 

 Thylacocrinus, Lampterocrinus, Eucrinus, and Sagenocrinus, 

 these genera, without exception, have underbasals, and Zittel 

 discriminated distinctly between genera in which the calyx is con- 

 structed exclusively of three rings of plates, and those in Avhich 

 the radials are separated by interradials — our Sphferoidocrinidae 

 — and he distinguished these from our Ichthyocrinidae. He, how- 

 ever, placed Dimerocrinus with some of our Actinocrinidae, as 

 that genus was thought to possess no underbasals, and he for a 

 similar reason admitted Lyriocrinus among the Calyptocrinidae. 



The Glyptocrinidte and Rhodocrinidae of Zittel, according to 

 his own diagnosis, differ only in the form of the body and the 

 position of the interradial (not anal) plates. He describes the 

 form of the Glj^ptocrinidse as high (turbinate), that of the other- 

 bowl-shaped (more or less depressed), the first interradials of the 

 former as being placed between the second and third radials, those of , 

 the latter as forming together with the first radials a ring of ten 

 alternating plates. We doubt very much whether these dif-- 



' Traite de Paleont., 1857, vol. iv. 

 -Lethsea Geogn., 1855 (Ausg. 3). 

 ^ Handbuch der Palseontologie, i. 



