INVERTEBRATES. 329 



CHOLASTEE PECULIABIS, Sp. nov. 



PI. XXXI. Fig. 4. a. Dorsal view, natural size; I. Section of a ray enlarged, showing 

 the arrangement of the plates. 



The general form of the body is that of a truncated pentagonal 

 star, with a large circular disc. A centro-dorsal plate is surrounded 

 by five others, all of which are much larger than other plates of 

 the body, and occupy a centro-dorsal depression. The position of 

 these five plates is that of radials, resting upon a basal, and there- 

 fore, all other plates of the body might be regarded as radials and 

 interradials, the latter being very numerous, because of the wide 

 separation of the rays at their junction with the body. The inter- 

 radials are polygonal, convex, or subspinous plates, without much 

 variation in size whether filling the larger or smaller interradial 

 spaces. The plates following the larger radial plates, as above de- 

 fined, in the direction of the rays, are not, however, by their form 

 or arrangement to be distinguished from the interradials, though 

 differing from those forming the rays. The plates covering the 

 dorsal side are thus divided into three kinds, viz. : First, the larger 

 plates filling the centro-dorsal depression; second, the disc plates 

 which cover all other parts of the body except the rays, and, third, 

 the plates which cover the rays proper, which in this species are 

 easily distinguished from the central disc pla.tes. 



The rays are short, abruptly truncated, and slightly expanded at 

 the apices by reason of an enlargement of the terminal plates. 

 They are widely separated from each other, though not at uniform 

 distances, and present the appearance of having been stuck on 

 the central disc, instead of having grown from it, an appearance 

 more marked, by reason of the change in the form of the plates, 

 from the disc to the rays. 



One of the interradial spaces is much greater than the others, so 

 that a line may be drawn across the disc, leaving three entire rays 

 upon the smaller half. The back of each ray is covered by a series 

 of transversely elongated plates separated from the side series by a 

 longitudinally impressed line. A single series of plates covers either 

 side of a ray, interlocking with the transverse dorsal series and di- 

 rected backward toward the disc. 



The oral plates are unknown, and no madreporiform tubercle has 

 been detected. 



Position and locality: Same as the last. 



No. 2,480 Illinois State collection of 1880. 



