1879.] NATURAL SCIENCES OF PHILADELPHIA. 353 



support on their upper sloping sides two arms, which subdivide 

 once, or oftener. 



The arms ramify in the same manner as in Zeacrinus, by throw- 

 ing off branches toward the inner side of the ray ; they touch, 

 laterally, and are so arranged that the sutures between the rays, 

 from the basals up, form straight lines, except on the posterior 

 side where the arras curve slightly, following the margin of the 

 anal area. The arms, before they become simple, are composed of 

 short, strongly wedge-shaped joints alternately arranged, which in 

 most species are by degrees turned into a double series of inter- 

 locking plates. Pinnulse very small and short. 



The arrangement of the anal plates is exactly as in Zeacrinus 

 and Woodoci'inus, but the anal area is less protuberant. The ven- 

 tral sac, which is the most remarkable part of this Crinoid, and 

 the best character for distinction, has the form of a mushroom? 

 upright, cylindrical below, abruptly spreading beyond the tips of 

 the arms and forming a rim composed of a row of 6, 11, 15 or 

 more large, spiniferous or nodose plates, spread out horizonally 

 and tending slightly downward. The upper part or roof is low 

 hemispherical, and is formed either by the spiniferous plates them- 

 selves, which are in that case unusually large, or more frequently 

 by a number of irregular plates within the centre. The tube, or 

 cylindrical portion of the sac, is composed of small plates, hori- 

 zontally arranged, and provided at the sutures with one or two 

 rows of respiratory pores. No other aperture has as yet been ob- 

 served, nor has the connection of the tube with the main body 

 been ascertained. 



Column small. 



De Koninck, in his generic description, took the upper portion 

 of the ventral sac to be a regular vault, and thereby distinguished 

 this genus from Poteriocrinus with a large proboscis, while this 

 organ, as he supposed, was absent in Eydreionocrinus. Some of 

 the European species which De Koninck refers to his genus must 

 be considered doubtful until better proof is given that the}' belong 

 here. His H. globularis is, in our opinion, an Eupachycrinus. 



Eydreionocrinus has the closest relations with Zeacrinus, with 

 which it agrees in the construction of the calyx, and in the mode 

 of bifurcation of the arms ; but the enormous size of the ventral 

 sac, its peculiar form and construction, seem to warrant a full 

 generic separation. 



