FOSSILS OF THE KEOKUK GROUP. 515 



figure. It is the incurved extremity of the dextral right posterior ray 

 that has been mistaken for a sixth ray. The specimen is somewhat 

 crushed and distorted, but by carefully cleaning it and removing some 

 adhering portions of the matrix, this ray can be traced straight out to 

 the periphery, where it curves abruptly around and extends iuward to 

 near the middle of the posterior iiiterbrachial space, where it terminates 

 at a point near which was doubtless situated the so-called ovarian 

 pyramid, though the specimen is too much crushed there to show the 

 latter. 



It is worthy of note that our speries. although agreeing with most of 

 these that have been referred to Ayelacrinites.* in the imbricating char- 

 acter of its disc plates, as well as in the direction of the curvature of 

 its rays, still differs from A. Hamiltonensin, of Vanuxeui, the type of the 

 genus in both of these characters. VASUXEM: gives no description, but, 

 judging from his figure, (Geol. Report, Third District, X. Y., p. 306,) one 

 would naturally suppose the disc plates of his species to have the usual 

 imbricating arrangement. Prof. HALL, however, has recently described 

 it in detail, (Twentieth Report Regents Univ., X. Y., on State Cab. Xat. 

 Hist., p. 299, 1868,) and distinctly states that its iiiterbrachial 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 sinistral, and its left ante- 

 rior and posterior-lateral rays curved to the left, as shown in VAXUXEM'S 

 figure. It therefore certainly seems to us doubtful whether species dif- 

 fering in two such important characters as these are strictly congeneric. 

 If they are not, then a new generic name should be applied to our spe- 

 . and the others agreeing with it in the.se characters, in which case 

 we would propose to designate this group of species under the name 

 Lepidudiscm (Y"'^. a scale, and JtVrzo?, a quoit.) At least we should think 

 they ought to be separated siu>geuerically. 



Locality and position Crawfordsville, Indiana. Keokuk beds of 

 Lower Carboniferous. 



* By some oversight, Prof. PICTET figures, on pi. xcii, fig. 25. of his valuable Trait de Palaeont.. a 

 true Agdacrinites, and probably one of the Cincinnati species, under the name Hemicittitei pararitica, 

 Hall a very different fossil from the Niagara group. He also alludes to Vannxem's Agdacrinites 

 Hamiltontn*iii in the text as a Silurian species, but it is a Hamilton group (Devonian) fossil. Dujar- 

 din and Hupe iHi.st. Xat. Echinod.. pi. 5. fig. 8). copy PicTET's figure under the name Agdacrinites para- 

 titita. as an illustration of Agelacrinites. saying Hemicygtites ought not to be separated from Agdacri- 

 nitet. The real Hemicyttites paragitica, however, although related to Agelacrinites, differs in several 

 important characters. 



