2l6 XRW YORK STATE MUSEUM 



A tendency of these sutural canals to become oval in cross section 

 and with the major axis at right angles to the sutures is clearly seen 

 at several places in figure 3. It probably represents the effects of 

 the bending of the free ends of the b.v. to assume the most favorable 

 positions for the performance of their function, which would be 

 toward the freer area of the enlarging plate surface. It will be 

 seen that this influence has led not only to just such widening of the 

 sutural canals in Palaeocrinus and Palaeocystites, but it has been 

 followed by. an actual bifurcation of the b.vs. themselves. 



Plate a, text figure 3, also shows a periodic variation in thickness. 

 It was thin in its nepionic stage and thickened, particularly along its 

 horizontal sutures, during its adolescent stage. There was thus 

 left the two nearly central basins or shallow depressions, one on 

 each side of the axial fold, which represent the early lateral margins 

 of the plate. Either the impetus gained through the development 

 of plate thickness carried the form beyond the requirements of its 

 environment or the later environment became less exacting in this 

 respect, for during the ephebic stage the plate appears to have built 

 its edges with stereom of diminished thickness. To this third plate 

 stage is due the shallow basins at the corners which resemble the 

 nepionic basins nearer the plate centers. 



Palaeocrinus striatus Billings 

 Canadian Org. Rem. Dec. IV, 1859, p. 25, pi. i, fig. 5a-5b 



Cup analysis. Through the courtesy of the late Dr J. F. 

 VVhiteaves of the Geological Survey of Canada the writer has been 

 enabled to give long and careful study to Billings's type of this 

 genus and species. 



The cup analysis here given, figure 4, dififers very materially in the 

 form of its RA and adjacent plates, from the cup analysis given by 

 Bather in '* A Treatise on Zoology," part 3, p. 172, and also from the 

 very conventional analysis given by Billings, loc. cit. p. 24. Failures 

 to present a correct cup analysis of the genotype have been due to 

 very great difificulties presented by the specimen itself. It was evi- 

 dently found lying in the bedding plane with its anterior side upper- 

 most, as this surface is most weathered (fig. 6). Below this is a 

 belt more recently separated from the matrix and presenting some 

 plate details in great perfection (fig. 5). A knife seems to have 

 been used to free the attached posterior area by cutting under the 

 anal plate from the oral end. Portions of x and RA were cut nearly 

 or quite through and the surface lost. On final liberation post. B, 1. 



