134 



CHIM^EROID FISHES AND THEIR DEVELOPMENT. 



In the type specimens (e. g., one shown in fig. 113) we note that the calcified 

 "rings," which were compared to the "centra" of Chimaera, are not rings at all, 

 in the sense that they occur in, for example, Squaloraja, but suggest rather a series 

 of more or less irregular lines of growth. These, indeed, are not transverse to the 

 long axis of the fossil, but at one side pass obliquely into root-like processes, com- 

 pared by Walcott to "lateral rib-sockets or supports," structures which, it must be 

 admitted, are altogether unknown in chima^roid anatomy. The foregoing evidence, 

 accordingly, seemed inadequate for associating this fossil with Holocephali, and an 

 examination of the types in Washington did not yield me any more convincing 

 basis of comparison. Nevertheless the very suspicion of a Silurian Chimaeroid was 

 of sufficient interest to warrant an attempt to secure more perfectly preserved 

 material. 



Accordingly, in 1896, I took the opportunity of visiting the type locality, and 

 may now add the following details : 



The horizon, the age of which is now generally admitted to be Ordovician, was 

 readily located, and Dictyorhabdus was found to be fairly abundant. A day's 

 collecting trip made in company with Mr. Burbadge of Canon City, to whose kind 

 guidance I am greatly indebted, resulted in obtaining about a dozen "columns" in 

 lengths averaging between one and two inches, together with numerous fragments; 



Distribution of Chimceroids in Time. 



