MORPHOLOaiCAL PART. 



137 



tween the arms to their full length, which in Symhathocrinus is composed of 

 elongate quadrangular pieces. The tube rests upon the upper faces of the 

 posterior radials, and extends to the tips of the arms. Hajjlocrinus, as we 

 understand it, has a simple anal opening, piercing the upper half of the 

 posterior oral. Cupressociinus ^. has a well-defined aperture between the 

 muscle plates of two adjoining radials. 



The anus of the Inadunata Fistulata has been observed in but a few 

 instances, and then only in the Cjathocrinidse, the Poteriocrinidae, and in 

 the embryonic Hyhocrinus and Oarahocrinus, In all of these cases, the open- 

 ing was apparently covered by a rather large, rounded pyramid of eight or 

 more pieces, which resembles the anal pyramid in the Cystids. In Oaraho- 

 crinus, in which the ventral disk remains permanently in the larval state, 



Fig. 1. 



Fig. 2. 



Carahocrinus. — Pig. 1. Ventral aspect. Eig. 3. Dorsal aspect. 



U = radials ; R' = radiaiial ; x = anal ; xp = anal pyramid ; o =■ orals. 



having five large orals similar to those of the Larviformia, and subtegminal 

 ambulacra, the pyramid is excentric and directed upwards (Figs. 1 and 2 of 

 the accompanying diagrams)."^ A similar anus was observed by W. R. Billings 

 in Hyhocrinus conicus. In Cyatliocrinus we have observed the anal pyramid 

 in several species, and found it located in all of them at the end of the tube, 

 directed anteriorly (Plate YII. Figs. 11 ab and 12 ah). The anus of the Pote- 

 riocrinidae, which we have seen in Poterioerinus, Decadocrinus, and in several 

 species of Scytalocrinus and jScaphiocrmus, is located at some distance from 

 the top of the ventral sac, and invariably at the anterior side, sometimes 



* These diagrams were made after drawings by Mr. Walter R,. Billings, The specimen of Fig. 1 is in 

 the collection of Mr. J. Stewart, that of Fig. 3 in his own collection. 



18 



