1885.] NATURAL SCIENCES OF PHILADELPHIA. 265 



the first radials, the posterior interradial takes the functions of 

 the anal plate, and the second order of interradials, which consists 

 of two pieces, generally contains the second anal with additional 

 plates above. The anals, as a general rule, are arranged longi- 

 tudinally, hut the row is often interrupted by intervening inter- 

 radials. In Reteocrinus, in which the interradial series consists 

 of small irregular pieces, the posterior side is divided equally by 

 a vertical row of large convex anals, arranged like the plates 

 which constitute the dorsal side in the tube of Catillocrinus. 

 The only essential difference between the two structures is that 

 the plates in the latter form a free appendage, similar to that of 

 Thaumatocrinus, while those of Reteocrinus and Xenocrinus are 

 incorporated into the calyx. 



All typical Actinocrinidse, Glyptasteridae, Barrandeocrinidre, 

 Acrocrinidse and Hexacrinidae have a special anal plate between 

 their first radials, and in most of them the first posterior inter- 

 radial is split into two halves to receive the second anal plate. 

 However, in Actinocrinus and allied genera which we separated 

 under Actinocrinites, the second anal is pushed up to the line of 

 the secondary interradials, although the first interradial, as in the 

 other groups, is divided. The splitting of the first interradial for 

 the reception of an anal piece, to which we have alluded, is of the 

 utmost importance for the study of the summit plates, as we find 

 the same thing there repeated among the proximals. 



In the Meloerinidae the first interradials are undivided, and 

 in most of them the lower anal plate is inserted between the two 

 secondary interradials ; in others, however, which have no anals 

 within the dorsal cup, the anals commence at the equatorial zone. 

 In the Platycrinidae the first interradial of the posterior side is 

 considerably larger, and evidently consolidated with the first anal 

 plate. In the Calyptocrinidae, finally, the whole calyx, dorsally 

 and ventrally, is strictly symmetrical, the anus central, and the 

 only asymmetry in their structure is found among basals and 

 proximals. 



The anal opening in all Camarata is located at the distal end 

 of the tube, whether this terminates within the calyx or is ex- 

 tended into a proboscis, and its position is more or less lateral, 

 except in the Calyptocrinidae in which it penetrates the central 

 piece. The plates composing the tube of the Camarata are ab- 

 actinal, and form a part of the posterior interradial series ; they 



