DESCRIPTIONS OK SOME NEW in.ASTOIDS. 89 



Basals deeply imbedded within the cokimnar cavity, the outer angles 

 barely reaching the margin. Radials comparatively small; length 

 twice their width at tlie basi radial suture, gradually increasing u[)ward, 

 SO that the forks or limbs at their upper side are about ei[ual in width 

 to the body of the plate at its lower side. The lateral sides are some- 

 what thickened at the upi)er face of the edge, more particularly toward 

 the lower end of the plate, where they produce indistinct ridges at the 

 suture lines. The upper side of the limbs is gracefully curved in an 

 upward direction, with reentering angles toward the lateral sutures, 

 and deeper ones toward the radial sinuses. From the bottom of the 

 |)late there e.NLtends to the radial sinus (which, in this species, is about 

 half-way to the toj) of the liml)s,) a conspicuous rounded ridge, ending 

 in a very prominent lip; and it is this structure mainly which {produces 

 the truncation toward the basal region, which otherwise would not be 

 very iierceptible. 



Interradial or deltoid pieces large, measuring almost four-fifths the 

 length of the body; broad lanceolate. Four of these have a length 

 equal to twice their greatest width. The fifth, that of the posterior 

 side, which in this genus is divided throughout its full length by a large 

 anal plate, occupies, including the latter piece, no greater width than the 

 four regular interradials, and the two halves are narrower at any place 

 than the interposed anal [)late. The latter is lanceolate, of nearly 

 equal width throughout, slightly tai)ering at the u^iper end. Its lower 

 side rests on the same surface with the other plate, but gradually rises 

 above the general level, and at the top is highly elevated, standing out 

 cons[)icuously over the adjoining |)arts. I^\'en in height it extends be- 

 yond the limits of the other parts of the body. 



Anal ai)erture large, oval in form, horizontal in position. Toward 

 the outer side, the opening is formed by the wall of the anal plate, 

 which at the upi)er end is bulging outward without being excavated. 

 The lateral sides of the aperture are formed by the ui)per curved ends 

 of the interradials, which are connected by two or three small anal 

 vault-pieces, and these constitute the upper boundary of the aperture. 



Ambulacra long, narrow, linear, raised above the general level of the 

 body, except close to the oral pole, near which they curve abruptly 

 toward the oral opening, and the ambulacrum becomes located below 

 the abutting surface. The lancet-jiiece is deeply grooved along the 

 median line, and when the side-pieces (pore-pieces of Roemer) are not 

 in i^lace, there is at the suture, along each side of the plate, a deep 

 sulcus, penetrated by the hydrospire-pores. This sulcus, however, 



[Pkoc. D. A. N. S., Vol.. IV.] 12 [Sept. 30, 1884.] 



