350 PROCEEDINGS OF THE ACADEMY OF [1879. 



elliptic as in that genus. The whole protrudes and is almost even 

 with the surface of the adjoining arms, which curve around it or 

 rest upon its flanks. The ventral sac is broadly balloon-shaped, 

 and extends, so far as observed, to about one-half the height of the 

 arm. It is composed of a great number of small plates, is sub- 

 pyramidal, sharply pointed at its upper end. It consists of five 

 diverging spheromeres, the radial portions deeply depressed, the 

 interradial extending outward in sharp edges, the edge at the 

 posterior side connecting with the anal area, those of the other 

 sides abruptly turned near the top of the calyx toward the poste- 

 rior of the specimen, where the sac evidently connects with the 

 main bod}', thus resembling a balloon. The sharp edges are 

 wedged in for a short distance between the outer arms of two dif- 

 ferent rays, and the arms themselves with their pinnube rest 

 within the radial excavations almost as in E ucalyptocrinus. The 

 radial spaces are subdivided near their base by a short ridge, 

 underneath which, and apparently independent of the sac, there is 

 seen in every ray a little short tube representing the ambulacra] 

 passages. There is no sign of an anal opening, but we have ob- 

 served two rows of respiratory pores along the median line of the 

 radial depressions. 



Column round, sometimes bordered by irregular lateral cirrhi; 

 its diameter small, the central canal minute and apparently round. 



The genus Zeacrinus is evidently closely related to Woodocri- 

 nus, and as we are inclined to believe that the ventral sac, which 

 has not 3*et been discovered in the latter, is most probabty simi- 

 larly constructed, we have felt almost like placing Zeacrinus 

 (which was defined as late as 1858 by Hall), under De Koninck's 

 genus as a subgenus. We have noticed, however, a difference in 

 the construction and habitus of the arms by which we think the 

 two may be satisfactorily distinguished. Those of Woodocrinus, 

 as observed in a large number of specimens, show a strong inclina- 

 tion to separate by being more or less irregularly bent to one side, 

 particularly near the top; while in Zeacrinus they are closely 

 folded up, very much as in Ichthyocrinus, and perfectly straight, 

 with quite a different mode of bifurcation. In the former they 

 are round, very robust, terminating in a sharp point; in the latter 

 almost flat, veiy delicate, and of nearly uniform size throughout. 



The identification of Zeacrinus lias always been attended witli 

 difficult}-, owing to the fact that it had not been sufficiently well 



