1888.] NATURAL SCIENCES OF PHILADELPHIA. 385 



and all converge into one in the second radials, thence passing down- 

 Avard along the inner surface of the first radials toward the basals. 

 The bifurcations near the calyx are unequal, the sloping faces of the 

 axillaries next the outer margins of the rays being considerably 

 wider than the inner ones, and the plates which they support are as 

 large in proportion. This continues on to about the sixth axillary, 

 above which the bifurcations gradually become regular, and the 

 outer plates attain the same width as the inner ones. By this peculiar 

 arrangement there appear, when the arms are spread, along the outer 

 plates of adjacent rays, five well marked lanceolate areas, to the top 

 of which the rays remain in lateral contact. The bifurcations along 

 the arms are extremely numerous, and take place at various inter- 

 vals, sufficient to fill up the full segments of the circle when the arms 

 are extended ; they taper but slightly, are very long, and become 

 thread-like at the ends. 



The higher radials from the first primary up project inwards, beyond 

 the periphery of the calyx ; the second projects the farthest, and the 

 plates of the second order slope away from it, as also those of the 

 third. The latter form the proximal ends of the lanceolate areas 

 whose overhanging margins, together with the outermost interradial, 

 form a roof, under which are located five large recesses or chambers, 

 interradial in position, each of which is occupied by two sets of lami- 

 nated structures, in form and arrangement closely resembling the 

 hydrospires of the Blastoid genus Oropkocrinus. Each set apparently 

 is composed of five to seven folded lamellae with continuous walls 

 and loops at each end ; they stand upright, face laterally the inner 

 walls of the overhanging primary radials, their upper ends attached 

 to the inner floor of the outer interradial, being thus completely 

 covered by vault structures. 



Vault flat, on a level with the spreading arms ; composed of five 

 oral plates (the so-called central plate and the four large proximals). 

 The posterior oral (central plate) is large, somewhat elongate, its an- 

 terior end resting between the truncate faces of the four others, the 

 posterior end againt small anal plates. The four small orals vary 

 from elongate-clavate (PI. XX, figs 2^ and 4) to almost regularly 

 hexagonal (PL XX, fig. 3). Outside the orals, and alternating with 

 them, are five somewhat irregular radial plates, which are axillary, 

 giving off" two sets of covering pieces, two rows of plates to each set, 

 all in lateral contact ; they are heavy, convex plates, a little wider 

 than high, alternately arranged, and solidly inserted into the vault. 



26 



