TAXOCRINIDAE 34/ 



IBB large, erect, forming part of calyx wall. BB the largest plates in 

 calyx. RR and succeeding Br sharply arched and angular, becoming more 

 rounded above, and somewhat flattened distally; height to width of IBr, 3 to 2.5. 

 iBr one, large, followed by two small plates, and others above tapering to a point 

 above which the rays meet closely as far as the IIIBr. No illBr. IIBr 5, about 

 as wide as long, with straight sutures. Higher brachials to third bifurcation 

 wider than long, the sutures becoming sharply arcuate distally. Column at base 

 of calyx as large as infrabasal disk, diminishing distally, and columnals gradu- 

 ally increasing in length. Anal structures not disclosed by the specirnen, but no 

 doubt as in P. laevis. 



No specimen but the type has been found that is clearly referable to this species as above 

 defined. All others similar to it found in Canada are smaller, and have been referred to 

 P. laevis. A marked peculiarity in the original specimen is a distal flattening of the arms 

 above the last bifurcation, with a sort of longitudinal depression which gives the arm at this 

 point a superficial appearance of being biserial, or of having a median groove as on the 

 ventral side. The latter interpretation was put upon it by Wachsmuth and Springer (Rev. 

 Pal., pt. 3, p. 201), who considered it as a recurrent ambulacrum like that of Hybocystu, 

 and this was thought to be present also in P. laevis. Careful examination of the type and 

 eight other specimens of laevis fails to disclose any such structure as in the type of elegans. 

 In the latter it certainly has much the appearance of a recurrent ambulacral groove, as before 

 supposed, but there is no trace of covering plates, or of the sockets for them. After com- 

 parison with many specimens of Hybocystis in which ambulacra of that kind are well pre- 

 served, I think this must be treated as merely a superficial resemblance due to the sharp 

 median curvature of the sinuous sutures, combined with some flattening of the arms. 



The arms, though not fully preserved, apparently taper to fine distal ends as in P. laevis 

 (PI. XLV, fig. 4b), which is inconsistent with the idea of recurrent ambulacra as I have 

 heretofore described and figured them (Geol. Surv. Canada, Mem. No. 15P, 1911, pi. 2). 

 However caused, this appearance may be a specific character of P. elegans. A marked 

 character of the species is the large and erect infrabasals, which it shares with laevis, and in 

 which it resembles the Lecanocrinidae division of the Sagenocrinoidea. The general out- 

 line of the two species is also strongly similar to that of certain Dendrocrinidae. The type 

 of P. elegans is much flattened, giving it a much broader appearance than the real form as 

 shown by measurements from which the dimensions above given are taken. 



Type. In the Victoria Memorial Museum of the Geological Survey of Canada, Ottawa. 



Horizon and locality. Ordovician, Trenton limestone ; Ottawa, Canada. 



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