332 PALAEONTOLOGY OF ILLINOIS. 



normal development of the plates in Lepidesthes, however, could not 

 produce such protuberances at the apical end, because the imbri- 

 cation of the plates is downward and would not permit it. Had we 

 other specimens showing an irregular development of the ambulacral 

 areas and great increase in the number of plates towards the apical 

 end, we would couple this feature with the remarkably developed 

 jaws, and refer the genus to a new and distinct family under the 

 name of Hybochinidce. At present we leave it in a family where it 

 seems to have at least some affinity. It is quite unnecessary to com- 

 pare it with any other genus, or for the purposes of identification 

 to continue the comparison with other characters possessed by 

 Lepidesthes. 



HYBOCHINUS SPECTABILIS, Sp. nov. 



PI. XXXI, fig, 5 a.; view of a depressed specimen as It appears on n slab, showing 

 parts of four ambulacral, and three interambulacral areas, a peculiar horn-like protuber- 

 ance and the protrusion of the jaws; fig. 5, b., view of the interambulacral plates and two 

 ranges of ambulacrals on each side near the apical end, magnified two diameters, some 

 of the scattering spines from the interambulacrals are also indicated; fig. 5, c., magnified 

 view of the ambulacral or other plates as they are thrust out in the horn- like protuber- 

 ance; fig. 5, ;d., magnified view of some of the ambulacrals and adambulacrals; fig. 6, 

 summit of a crushed specimen showing the jaws; fig. 7, jaws that may belong to this, or 

 a kindred species. 



General form subspheroidal, modified, however, by the extreme 

 flexibility of the test, and as it appears, 'in the type, at the apical 

 end, by peculiar protuberances, one of which projects like a horn. 

 Ten ranges of plates may be counted in an ambulacral area in the 

 type specimen, but this number may be, and probably is, exceeded 

 in the equatorial region, for ten ranges may be distinguished in the 

 horn-like projection from one of them, where all the ranges are 

 certainly not exposed. The ambulacral plates imbricate from below 

 upward, each exposing a somewhat regularly hexagonal area, trans- 

 versely elongated, in the central part of which there are two pores. 

 As the plates imbricate upward the lower part of each is covered, 

 so that, in fact, the pores occupy an upper central position in each 

 plate, passing through at the lower inner edge of the succeeding 

 one. The plates are so beveled as to form a smooth exterior to the 

 body. The interambulacral areas are lanceolate, a little more than 

 half as wide as the ambulacral areas, and consisting, as shown in 

 our specimen, at a point above the equatorial region, of five ranges 

 of plates. The ranges decrease in number toward the poles, and 

 the plates slightly diminish in size. The plates imbricate down- 

 ward, and from the central range outward, so that they overlap the 



