INVERTEBRATES. 289 



two of which it is placed so as to rest upon the basal pieces in 

 a notch at the posterior end of the suture separating the latter. 

 Second radials very minute, or apparently sometimes obsolete ; 

 when present occupying a small depression at the middle 

 of the upper side of the first radial pieces. Secondary radial 

 pieces small, and not always readily distinguished from the 

 first brachial pieces — resting either in part or entirely upon the 

 first radials, owing to the minuteness or absence of the second 

 radial pieces; supporting above, the brachial pieces, the inner 

 two of which, however, sometimes rest in part upon the small 

 second primary radial, and the outer two, in part, even down 

 upon the first primary radial. Interradial pieces small or 

 wanting, and not, when present, very distinct from the vault 

 pieces; never more than slightly truncating the superior lateral 

 angles of the first primary radials. 



Interbrachial appendages (wing or lobe pieces of Lyon), in 

 the typical species very large, and a rising from between the 

 inner arm-bases; sometimes thin and knife-like, and in other 

 species greatly thickened and bipartite — often nearly equaling 

 the length of the arms, but sometimes shorter, or probably in 

 some species obsolete. 



Arms, so far as known, four to each ray, and, excepting at 

 their immediate bases, composed each of a double series of very 

 short alternating pieces, each one of which supports a tentacle ; 

 not bifurcating after the divisions at their bases. 



Vault, according to Mr. Lyon, composed in the typical spe- 

 cies of comparatively few pieces, and having the opening 

 nearly central. In other species apparently falling within this 

 genus, the opening is lateral. Column apparently round. 



As remarked in connection with the description of that genus, on page 167, 

 this type is related most nearly to Dichocrimts, though it differs in general 

 form, as well as in the structure and arrangement of all the parts above the 

 first radials. It seems to include species constituting two sections or subgenera, 

 the first or typical one of which is characterized by the greatly developed inter- 



37 Sept. 17, 1SC6. 



