﻿244 NEW YORK STATE MUSEUM 



area was thus extended slightly toward the left. A new photo- 

 micrograph was now made and a colored screen used in order to 

 show if possible the limonite-colored mud fillings. This photomi- 

 crograph is reproduced as figure 4 of plate 6. The subject is a 

 difficult one both for photography and for reproduction, but it is 

 hoped that the plate will present enough detail to be both of interest 

 and value. 



Palaeocrinus chapmani Billings 



P a 1 a e o cy s ti t e s chapmani Bill. Canadian Org. Rem. Dec. Ill, 

 p. 71-72. No figure. 



The description of P. chapmani given by Billings in no par- 

 ticular differentiates that species from P. s t r i a t u s - 1 The term 

 " radiating ridges " is not used by him to designate either the cov- 

 ered epithecal canals or the side walls of the latter when the covering 

 is removed, but is used simply to designate the larger and more gen- 

 eral relief features of the plate. Thus one of the " radiating ridges " 



1 " Description. The few plates of this species that have been collected 

 exhibit the peculiar character of the genus in a most interesting and satisfac- 

 tory manner. Without being acquainted with the structure of the plates, the 

 observer would almost unhesitatingly refer them to two very distinct species, 

 so great is the change in their appearance produced by the wearing away of the 

 external surface. The perfect plates resemble those of P . dawsoni, 

 inasmuch as the number of radiating ridges is the same as the number of 

 sides. The ridges are however of a different form. In P. daw- 

 soni they are narrow at the base, and the space between them is flat; 

 but in P . chapmani they are broad at the base, or roof-shaped, the 

 base of each spreading out to a breadth equal to that side of the plate to 

 which it extends. A perfect plate of this species, for instance one of six 

 sides, may therefore be described as presenting six furrows radiating 

 from the center to the six angles, these furrows gradually increasing in 

 depth and width as they recede from the center of the plate. Or it may 

 be characterized as exhibiting six roof-shaped ridges radiating from the 

 center to the sides, and i ./greasing in height and width at the base as they 

 approach the side. 



When, however, the external surface is worn away, the plates assume a 

 very different appearance. They then become covered with deep fissurelike 

 striae, like those of P . tenuiradiatus, to which they bear so close a 

 resemblance, that to the unpracticed. eye, they appear to be the same. They 

 can always, however, be distinguished by this character. The ridges or 

 partitions between the fissures, which terminate at the centers of the sides of 

 the plates, are the highest, those at the angles being the lowest; but in 

 P . tenuiradiatus it is the very reverse ; the angles of the plate are 

 more elevated than the centers of the sides." 



