366 PROCEEDINGS OF THE ACADEMY OP [1881. 



Revised Generic Diagnosis. — Calyx obconical, its symmetry 

 somewhat bilateral ; interradial and interaxillary spaces pro- 

 foundly depressed ; radial plates highly elevated into sti'ong 

 rounded ridges, which in outer appearance resemble arms ; they 

 bifurcate and follow the secondary radials, whence they pass 

 gradually into free arm joints. 



Underbasals five, well developed, extending beyond the column. 

 Basals five, large, protuberant, hexagonal, the upper side slightly 

 truncate and supporting the first series of interradial plates ; the 

 upper portions inflected, and involved in the interradial depres- 

 sions. 



Radials 3X5, those of different rays separated by interradials ; 

 the first and third pentagonal, the second quadrangular, as long 

 as the two former ones but narrower. The radials are highl}'- 

 elevated, forming a broad rounded ridge, which from the third 

 radial branches upward, following the secondary radials, and 

 downward from the first primar3'^ radials toward the basals. This 

 branching gives to the first and third radials a similar form, only 

 the direction of the branches reversed, the truncation taking 

 place from reversed sides of the plates. Secondary radials four 

 to five in the adult, a less number in young specimens; decreasing 

 in height upwards, quadrangular, shaped like arm joints, and like 

 them giving off pinnules, which in the adult are incorporated ^ 

 within the body. 



Arms ten, long, slender, rounded, bifurcating, composed of a 

 single series of rectangular or slightly wedge-formed pieces, which 

 give off on alternate sides rather stout, closely arranged pinnules. 

 Interradial series resting directly upon the basals, consisting of 

 a very large number of minute pieces, of irregular form, and with- 

 out definite arrangement ; the posterior area wider, with a con- 

 spicuous row of decidedly larger and more prominent special anal 

 pieces along the median part. Interaxillary plates almost as 

 numerous as the interradials, and of a similar character. The 

 peculiar depressed state of the interradial and interaxillary areae, 

 the irregularity with which their plates are arranged, suggests the 

 possibility that they were adapted to expansion by the animal. 



Vault composed of numerous, \&vy small and convex pieces, 

 with an elevation running to each arm base ; the plates in the 



^ See our remarks upon fixed pinnules in our general notes upon the 

 Sphseroidocrini dae . 



