﻿462 Canadian Record of Science. 



However this may be, in the Museum of the Geological 

 Survey at Ottawa there is a well preserved fish tooth from 

 the Upper Arisaig series at McDonald's Brook, near 

 Arisaig, N.S., collected by Mr. T. C. Weston in 1869. On 

 the evidence of large numbers of other kinds of fossils, the 

 upper portion of the " Arisaig series" is still held to be of 

 about the same age as the Lower Helderberg group of the 

 State of New York and the Ludlow group of England, but 

 no Devonian rocks are known to exist at McDonald's 

 Brook. 



The tooth itself, which is not quite perfect at either 

 end, is about eleven millimetres in height by about five in 

 breadth at the base. It is conical, slightly curved and 

 somewhat compressed, the outline of a transverse section 

 a little below the mid-height being elliptical, and its 

 surface is covered with a thin coat of a finely and longitu- 

 dinally striated enamel. The figure is a line drawing of 

 the tooth, as viewed laterally, with an outline of the 

 transverse section, both of twice the natural size. 



Judging by its external characters, this specimen seems 

 to be what is usually called a dendrodont tooth, and 

 therefore probably that of a crossopterygian, perhaps 

 allied to Holopty chins, though its fore and aft edges 

 are not trenchant. Only one specimen of it has been 

 obtained, so that no thin sections of it have been made, to 

 show its microscopical structure. As it does not seem 

 referable to any known species, it may be convenient 

 to call it provisionally Dendrodus Arisaigensis. 



If the limestones from which this tooth was collected 

 are, as there is every, reason to believe that they are, 

 of Silurian age, a second species can be added to the 

 vertebrate fauna of that system in Canada ; but if not, the 

 tooth ,is still of interest as indicating the possible 

 existence of Devonian rocks at a locality where such 

 rocks have not previously been recognized. 



