266 PROCEEDINGS OF THE ACADEMY OF [1881. 



the CtenocrinidiTe ; while Carpocrinus and Macrostylocrinus were 

 referred to the Cyathocrinidae. 



Zittel amended Actinocrinidse by admitting Periechocrinus^ 

 Erelmocrinus^ AUoprosallocrinus, StrotocriniiSj Sleganocrinus. 

 Agaricocrinus and Megistocrinus, partly, however, as subgenera 

 of Actinocrinus. He, like Roemer and Angelin, separated the 

 genera with four basals, and ranged Stelidiocrinus and Harmo- 

 crinus, which have five basal pieces, under a distinct family. 

 Zittel further excluded Carpocrinus, Hahrocrinus and Desmido- 

 crinus, species with single arm joints, for which he proposed the 

 name Carpocrinidse, and he placed under the Dimerocrinidaa 

 Marcostylocrinus and Dolatocrinus^ genera with three basals and no 

 anal plate in line with the first radials, and among these he admitted 

 Gytocrinus, which we have ascertained has four and not three 

 basals, and Dirtier ocrinus, which has underbasals. 



The fact that in those classifications the least mistake or mis- 

 conception as to the number of the basals, a diversity in the 

 position or distribution of the anal plates, or a slight variation in 

 the form of the arm joints, throws the genus from one family into 

 another, is in itself sufficient proof, that the divisions are arbitrary 

 and artificial. A classification based upon fossils should be as 

 simple as possible, resting upon a broad basis, and the family di- 

 visions should express important and evident structural features, 

 and be not dependent upon such trifling variations as the number 

 of basal plates, etc. 



We place among the Actinocrinidte all genera of the Sphan-oido- 

 crinidfB, which are constructed of basals (without underbasals) ; 

 3 X 5 — rarely 2 X 5 — primary radials, all forming a part of the 

 calyx; one or more higher orders of radials, with at least one, 

 but generally several additional interradial pieces beneath the arm 

 regions ; a vault composed of a large number of heavy plates in 

 contact with each other ; and we include species both with single 

 and double jointed arms. 



For greater convenience of study we arrange the genera under 

 six sections. 



a. Stelidiocrinites: The simplest form of the sub-family. General 

 symmetry more or less perfectly pentahedral ; calyx low ; basals 

 five or three ; second radials short ; anal and interradial area 

 scarcely distinct ; arms single or double jointed. 



h. Agaricocrinites : Symmetry decidedly bilateral ; calyx low ; 



