216 PROCEEDINGS OP THE ACADEMY OF [188G. 



inward. The outer ones of these projections are wing-like, rest- 

 ing against, and partly upon, the intcrradials ; the inner one 

 sword-shaped, their sharp point extended deeply into the ambu- 

 lacra! groove, so as to divide it, and to form a branch groove for 

 each main division of the rays. Stephanocrinus angiilatus evi- 

 dentl}'^ had ten arms to the ra}'', but the mode of branching 

 beyond the second radials is not well known. We found, how- 

 CA-er, in one instance the second radial succeeded by two other 

 axillaries. The arms are biserial, thin, short, pinnule-like, and 

 they cover the whole ventral surface. In length they do not 

 extend beyond the interradial processes, which apparently were 

 to protect these delicate organs. 



The intcrradials are comparatively large. They resemble in 

 form and position the deltoids of Codasler, Troostocrinus and 

 other Blastoids, in which, like here, no part of the plates is visi- 

 ble in a side view. Tliey extend to the top of the projections and 

 rest against the inner faces of two limbs, the suture running 

 downwards so as to divide the processes into an inner and outer 

 part. The plates are connected laterally with one another, but 

 not centrally. They leave in the centre a moderately large open 

 space, which in perfect specimens is filled by oral plates. The 

 lateral edges of the intcrradials are deflected, curvino; downward, 

 so as to form a wide and deep ambulacral groove, which on 

 approaching the inner end becomes deeper and narrower, and 

 toward the arm bases divides as stated above. The ambulacral 

 grooves are readily distinguished from the general gutter formed 

 by the protuberances. The3' contain neither hydrospires, nor 

 pores, nor other openings, but there seem to be small axial canals 

 at the arm bases. At each side of the ambulacral groove there is 

 a sort of depression, which forms a place of attachment for two 

 series of small, subquadrangular covering pieces, which form a 

 vault over the groove, leaving underneath a circular, compara- 

 tively large passage, which at one end communicates with the 

 arms, at the other enters the calyx beneath the edge of the oral 

 pyramid. The covering plates of the same series are so closely 

 anchylosed that they appear in the best specimens, even under a 

 magnifier, as two single plates, one at each side, as which the}^ 

 were figured by Hall. Their composite nature and alternate 



