<>KPKK III 



CRINOIDEA FISTULATA 161 



(Jurli-y. Although agivring with this family in a general way, they are readily dis- 

 tinguished from the typical forms by certain characters which they possess in common 

 with tin- K,i<-riniibn'. The dorsal cup is saucer-shaped, and composed of heavy plates ; 

 the articular faa-s of tin- radials are provided with well-marked muscular fossae ; tin- 

 arms vary fnmi Unix-rial to biserial within the limits of the same genus ; and the ventral 

 sat- is reduced to a small cone, extending but little above the level of the ventral di.-k. 



These genera, according to Wachsmuth and Springer, constitute, together with the 

 genus Encrinus, a group which is sufficiently distinct to be recognised as an inde- 

 pendent family. 



European writers, on the other hand, have almost without exception agreed in 

 a>MK-iating Encrinus in the same category with recent Crinoids ; the reasons for this 

 being -partly because it is a Mesozoic form, partly because it has axial canals along the 

 inner floor of the dorsal cup, and, finally, because anal plates are wanting. But the 

 imaginary line which was formerly conceived as separating the Palaeozoic from the 

 Neozoic Crinoids, has now been generally abandoned ; and as axial canals have been 

 found to exist among Palaeozoic forms as well as among the later ones, the only vital 

 distinction remaining is the presence or absence of anal plates. 



In point of fact anals are present in most of the above-named genera. Cromy- 

 ocrinus and Eupachycrinus have both an RA and IRA ; Phialocrinus has only the 

 IRA, and Ulocrinus only the RA ; but Stemmatocrinus and Erisocrinus agree with 

 Encrinus in having neither IRA nor RA. Hence, if the division between the Poterio- 

 crinidae and Encrinidae be established simply upon the presence or absence of anal 

 plates in the cup, Stemmatocrinus and Erisocrinus are necessarily included under the 

 latter family, and the remainder excluded. But if other characters be chosen as 

 criteria, such as the mode of articulation, and the reduction of the ventral sac, then 

 all of the above genera must be included in the same family with Encrinus. The latter 

 course appears preferable-; especially since the gradual disappearance of anals may be 

 regarded as a natural consequence of the decrease in size of the ventral sac. Adopting 

 this course, the family Encrinidae may be denned as follows : 



Calyx more or less saucer -sJiaped, with dicyclic base. Infrabasals Jive, small, generally 

 concealed beneath the top stem-joint. Articular faces of the radials forming a horizontal line, 

 and completely occupied by the first costals ; faces provided with large muscular fossae, and a 

 perforated transverse ridge. Costals one or two. Ventral sac rudimentary ; anal plates gener- 

 ally absent. Tegmen (in Encrinus) elevated, composed of ratJier heavy plates. Arms usually 

 ten, rarely five or fourteen ; pinnule-bearing. Carboniferous and Trias.] 



Cromyocrinus, Trautsch. (Fig. 267). Dorsal cup low, cup- or saucer-shaped. 

 IB moderately large, always projecting beyond the column. IRA large ; 

 RA barely touching the ventral sac ; no plates of the latter 

 entering the dorsal cup. Costals one to each ray. Arms 

 ten, rarely five ; uniserial or slightly interlocking from 

 opposite sides. Column round. Carboniferous Limestone ; 

 Moscow, Russia. Kaskaskia Group ; Mississippi Valley. 



Eupachycrinus, M. and W. Dorsal cup as in the preced- 

 ing genus, but the IB much smaller, and concealed by the 

 column. B large. IRA and RA both represented ; the 

 latter very large, and supporting a small plate of the ventral FJG 



tube, the lower part of which descends into the cup. Arms cromyocnnus'gioiuius 

 generally ten, rarely five or fourteen ; either uniserial, inter- M. and w Sub-car- 



' , . * ' . , J Tr . boniferous; Chesti-r, 111. 



locking, or biserial. Kaskaskia Group ; Mississippi Valley. Natural size (after Meek 



Ceriocrinus, White (Delocrinus, Miller and Gurley). a 

 Dorsal cup as in the preceding, but the posterior B more elongate than the 

 others, and supporting a small IRA ; upper end of the latter extending above 



VOL. I M 



