358 



PROCEEDINGS OF THE ACADEMY OF 



])Ose the difc plates of his species to have the usual imbricating arrange- 

 ment. Prof. Hall, however, has recently described it in detail, (Twentieth 

 Report Regents Univ. N. Y. on State Cab. Nat. Hist. p. 299, 1868), and dis- 

 tinctly states that its interbrachial or disc plates are not imbricating, as in 

 other species. He also mentions the fact that this typical species differs 

 from others in having its anterior and right anterior and posterior lateral 

 rays sinstral, and its left anterior and posterior-lateral rays curved to the 

 left, as shown in Vanu.Kem's figure. It therefore certainly seems to us doubt- 

 ful whether species differing in two such important characters as these are 

 strictly congeneric. If they are not, then a new generic name should be 

 applied to our species, and the others agreeing with it in these characters ; 

 ia which case we would propose to designate this group of species under 

 the name Lepidodiscus [KiTri;, a scale, and Sia-noc, a quoit). At least we should 

 think they ought to be separated subgenerically. 



Locality and position. Crawfordsville, Indiana. Keokuk beds of Lower 

 Carboniferous. 



ECHINOIDEA. 



Genus OLIGOPORUS, Meek and Worthen. 

 Oligoporus nobilis, M. and W. 



Large, globose, composed of very thick plates. Ambulacra nearly flat, or 

 slightly convex, and without proper furrows, narrow lanceolate in outline, 

 or only about two- thirds as wide as the interambulacral areas ; pore pieces 

 comparatively small, wider than high, those of the two outer rows rather 

 more irregular in size, and some of them a little larger than any of those of 

 the two inner rows ; pores two to each piece, forming four double rows, 

 those of the two outer ranges of pieces being placed near their inner ends, 

 and those of the inner ranges near their outer ends. Interambulacral areas 

 comparatively large, moderately convex, and composed of five rows of large 

 plates, all of which extend to the disc above, while the middle one ends within 

 about 0-65 inch of the oral opening below. Vent and apical disc much as 

 in Mdonites multipara Surface of all the plates, both ambulacral and inter- 

 ambulacral, ornamented with coarse granules, separated by spaces generally 

 a little wider than their own breadth, with sometimes a few smaller ones 

 between. Of these granules, about 40 to 60 may be counted on each of 

 the larger interambulacral plates. 



Height and breadth, about 3-75 inch ; breadth of ambulacral spaces, 0-60 

 inch ; do. of interambulacral areas, 1-06 inch. Height of largest interam- 

 bulacral plates, 0-26 inch ; breadth of do., 0-40 inch; thickness of do., 0-25 

 inch. 



The only specimen of this fine species yet known to us is mainly a silicious 

 cast of the interior. The connection of the plates, however, are so distinctly de- 

 fined by sharply raised lines formed by the silicious matter deposited in the 

 sutures between all of the pieces before they were dissolved, that the entire 

 structure can be made out as well as if the plates themselves had been preserved. 

 A few of the plates, however, or rather casts of their external surface, remain 

 so as to show the surface granules as well as the thickness of the plates them- 

 selves. 



The apical disc seems to be very similar, as already stated, to that of Meloni- 

 ies rnultipora, — the arrangement and comparative sizes, as well as form of the 

 ocular and genital plates, being much the same. In two of the latter, five 

 pores may be counted in each, while one other also shows obscure indications 

 of five pores and the other two had four each, as near as can be made out from 

 the little projecting points representing them in the cast. No satisfactory in- 

 dications of pores, however, are to be seen in the ocular pieces. 



Although the ambulacral areas are not properly furrowed, as in 0. Dance 

 and Mdonites rnultipora, they are slightly depressed below the most convex cen- 



[Dec. 



