112 PROCEEDINGS OP THE ACADEMY OP [1886. 



crinus resembles Rhizocrinus^ but it differs from that in having 

 a strong porous ventral sac. 



Zittel's C3^athocrinidjie include Ci/athocrinus, Nipterocrinus^ 

 Barycrinus, Euspirocrinus, Ophiocrinus, Botryocrinus^ Palseo- 

 crinus^ Garabocrinus, Sphserocrinus and Pachyocrinus (Billings, 

 not Eichwald). with the following famil}^ diagnosis : Calyx 

 globose; basis dicyclic, composed of five underbasals and five 

 basals ; anals 1-3; arms strongly developed, single-jointed, long, 

 branching, without pinnules ; ventral side covered by " oral 

 plates." From his list must be excluded Nipterocrinus, which 

 has interradials and only three underbasals, and Pachyocrinus, 

 which is too imperfectly known to determine its position. There 

 are besides Sicyocrinus, Ophiocrinus, Botryocrinus and Bary- 

 crinus, in which the arms, throughout their whole length, give 

 off armlets at intervals, which evidentlj^ take the place of pin- 

 nules if they are not true pinnules themselves. We direct atten- 

 tion to this point, as both Zittel and De Loriol make the absence 

 of pinnules in the Cyathocrinidae the sole distinction between 

 this family and the Poteriocrinidse. 



The presence or absence of pinnules has been considered by 

 us heretofore as a doubtful character for distinguishing families. 

 The pinnules are extensions of the arms, and in their organiza- 

 tion, both morphologicallj^ and physiologically, almost identical 

 with the arms. They are short branchlets given off along the 

 sides of the arms, but ordinarily'- not extending to their tips. 

 The pinnules differ from arms only by their containing the fertile 

 portions of the genital glands, while the arms lodge the genital 

 cord. The branches of the arms may be said to be modified 

 pinnules, which differ from true pinnules in their greater length 

 and thickness. They are usually called arms when attaining the 

 form and length of the primary arms, but armlets when shorter, 

 less robust, and given off at regular intervals. Frequently the 

 branches are pinnule-bearing again, and this is the case in the 

 Poteriocrinidae, in which all arms, whether branching or simple, 

 main arms or side arms, are fringed with true pinnules. The 

 presence or absence of pinnules would prove to be a much better 

 character for distinguishing the two groups, were it not that 

 Barycrinus and allied genera represent a most perplexing transi- 

 tion form in having short side branchlets, given off at regular 

 intervals, and these branching off once or twice again in a similar 



