FOSSILS OF THE BURLINGTON GROUP. 455 



small second radial, and partly on the first radial beneath, 

 and each supporting two slightly larger pieces, the last of 

 which is an axillary piece, and bears an arm on its outer 

 sloping side, while the inner bears two pieces in direct 

 succession, the second of which is axillary and bears two 

 anus, thus making six arms to each of the rays; interradi- 

 als of moderate size, hexagonal in form, longer than wide, 

 and wider below than above. 



Vault moderately and regularly convex, and composed 

 of unequal tumid pieces, four or five of which in the cen- 

 tral region are much larger than the others; opening deci- 

 dedly lateral, and directed horizontally outward, occupying 

 a protuberance composed of small pieces, and placed nearly 

 on the same horizon as the arm-bases. Sutures between 

 the body plates more or less distinctly furrowed. Surface 

 smooth or only granular.* Column rather stout, and show- 

 ing the compressed and twisted character of the genus very 

 distinctly, composed of pieces of nearly uniform thickness. 



Hight of body to top of vault, 1.52 inches; breadth, 1,20 

 inches. 



We have referred this specimen to P. Hattl, of Shumard, with some 

 doubt, because in some of its characters it seems to be quite as nearly 

 allied to P. incomptus, of White. It differs, however, from authentic 

 specimens of Dr. WHITE'S species now before us, in the much less de- 

 pressed form of its body and base, its proportionally longer first radial 

 pieces, and decidedly smaller second radials, in all of which characters 

 it seems to agree more nearly with the description of P. Halli (= P. 

 olla, of Hall.) The specimen we have figured has lost its arms, as 

 seems to have been the case with the one from which Prof. HALL'S de- 

 scription was drawn up; enough of the free parts of the rays remain, 

 however, to show that there were almost certainly three arms to each 

 main division of each ray, or thirty to the whole series. 



Other specimens in Mr. WACHS^irTii's collection, believed to belong 

 to this species, show three arms to each division of each ray, and in 

 these the arms are rather long, and not sensibly thicker in the middle 

 than at the base, while they show the peculiarity of having along each 



* The specimen figured shows on the base, and some parts of some of the first radial pieces, indica- 

 tions of a few rather irregularly scattered nodes; hut as these are clearly produced by some little 

 bonus parasite, (being each with a little pit in its top.) we have not represented them in the figure. 



