NATURAL SCIENCES OF PHILADELPHIA. 357 



Genus AGELACRINITBS, Vaiuixem. 

 Agelacrinitks (Lepidodiscus) squamoscs, M. and W. 



Depressed discoidal ; outline circular, or somewhat oval. Rajs slender, 

 long, and strongly curved as they radiate from the middle toward the periph- 

 ery, around which they are each extended for some little distance ; all sinis- 

 tral excepting the right posterior one, which curves to the left, with its outer 

 half extending around within that of the next one on the left, near which it 

 terminates at the so-called ovarian protubrance ; each composed of two zigzag 

 rows of very small pieces, with some irregular ones apparently not belonging 

 properly to either row. Disc composed of large, thin, irregular, strongly 

 squamose or imbricating plates, the imbrication beinginward from the periph- 

 ery, that is, the inner edge of each plate laps upon the outer edge of the next 

 within. Ovarian? pyramid situated near the left outer margin of the posterior 

 iaterbrachial space, and closed by ten pieces, apparently imbricating laterally 

 and forming a depressed cone, around the base of which there are numerous 

 small, short, but comparatively wide imbricating disc plates. Surface minutely 

 granular. 



Greater diameter of an apparently distorted specimen, 1-70 inch. 



The only specimen of this species we have seen is somewhat crushed and 

 distorted, so that it is rather difficult to make out the exact details of the 

 structure of the rays, though they are apparently not provided with open 

 ambulacral furrows, the rows of minute plates on each side, apparently closing 

 up and interlocking. There appear, however, to be pores arranged along 

 them in a zigzag row between the pieces. The body plates around the mar- 

 gin are much wider than high, and strongly imbricating upward. No cen- 

 tral opening is visible. 



On comparing this species with A. Kashaskiensis, Hall (the only other 

 known Carboniferous species), the type of which is now before us, we find 

 that our species differs in the important character of having its disc plates 

 all very distinctly imbricating, while those of Prof. Hall's species show no 

 tendency to imbricate, the whole surface of each being clearly exposed, their 

 straight edges being merely joined together like those of a true crinoid. 

 From Prof. Hall's description, it might also be supposed that this species 

 tlitfers in the number of its rays, as he described it as having six rays. 

 A careful examination, however, of the typical specimen has clearly satisfied 

 us that this is certainly not the case, as it has only five, the usual number, 

 &i represented in the 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 remov- 

 ing some adhering portions of the matrix, this ray can be traced straight 

 out to the periphery, where it curves abruptly around and extends inward to 

 near the middle of the posterior interbrachial 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 species, although agreeing with most of 

 these that have been referred to AgeLacrhiUes* in the imbricating character 

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

 still differs from A. BuinUionensis, of Vanuxen, the type of the genus in 

 both of these characters. Vanuxem gives no description, but judging from 

 his figure, (Geol. Report Third Dist. N. Y., p. 306) one would naturally sup- 



* By pome oversight, Prof. Pietet figures, on pi. xcix, fig. 25, of his valuable Trait de 

 Palffiont., a true Agelaariniles, and probably one of the Cincinnati species, under the name 

 Hemici/ftiles parasUica, Hall, a very different fossil from the Niagara group. He also alludes 

 to Vanu.xem's Agekicrinites HamiUonensis in the text as a Silurian species, but it is a Ham- 

 ilton group (Devonian^ fossil. Dujardin and Hupe (Hist. Nat. Echinod. pi. 5, fig. 8) copy Pie- 

 tet's figu'-e under the nume Arjdacrinites parasitica, as an illustration of Agelacrinites, saying 

 Hemicystites ought not to be separated from AgHncrimtes. The real Henua/slites parasit.cu. 

 however, althougli related to AgfiacriniUs, differs in several important cfiaracters. 



1868.] 



