﻿REPORT OF THE DIRECTOR I9IO 



245 



of his P. chapmani (see upper left-hand region of text figure 

 20) consists of a long, high, large, central, covered epithecal canal 

 with the younger, shorter and smaller canals grouped on either side 

 of it. These all crossed the suture and so form a ridge " broad at 

 the base, or roof-shaped." The canals themselves Billings calls 

 " deep fissurelike striae " and, as shown by our figure, a " radiating 

 ridge " may consist of a group of seven or eight of these fissurelike 

 striae. His whole description, given in the footnote, tells us only, 

 so far as concerns the descrip- 

 tion of the species, that it ex- 

 hibits " six roof-shaped ridges 

 radiating from the center . . . 

 and increasing in height and 

 width ... as they approach 

 the sides. When . . . the 

 external surface is worn away, 

 the plates . . . become cov- 

 ered with deep fissurelike striae, 

 like those of P. tenuiradia- 

 tus." We may express the 

 essence of the description as fol- 

 lows : the plates of P. chap- 

 mani show as many radiating 

 groups of covered canals as 

 there are angles to a plate. The 

 older, central canals are higher fig. 20 From a photomicrograph (xio) of. the 



dl j r i.1 holotype of Palaeocystites chapmani 



longer and troll! these We Bill., now in the Museum of the Geological Sur- 



1 1 1 vey of Canada at Ottawa 



may pass down a regular slope 



to the smallest and shortest canal which is always situated next to 

 the angle of a plate. His means of distinguishing between his P. 

 chapmani and P. t e nu i r a d i a t u s Hall is but a means of 

 distinguishing between his Palaeocrinus s t r i a t u s and 

 Hall's Palaeocystites tenuiradiatus. 



The holotype consists of a single plate so badly weathered as to 

 lose some portion of the entire surface and very much of that sur- 

 face as the plate margins are approached. A small portion of the 

 sutural faces is also lost. If we examine in detail the figure of the 

 type, here given, we may note the following resemblances to the 

 r,ant.B of Palaeocrinus striatus. 



