26 THE CANADIAN NATURALIST. [Yol. X. 



with a brief diagnosis of its most salient characters, as follows : 

 premising that a more detailed description of the species, accom- 

 panied with figures, will appear at an early date in one of the 

 publications of the Canadian Geological Survey. 



Pterichthys (Bothriolepis) Canadensis, nov. sp. — Plas- 

 tron nearly flat. Helmet moderately arched above, most promi- 

 nent immediately behind the orbital cavity where it rises into a 

 ridge or blunt keel, which is continued, at intervals, with greater 

 or less distinctness, along the median line of the buckler. Buck- 

 ler slightly arched, median keel strongest in the centre of the dor- 

 somedian plate, and in the posterior half of the post-dorsomedian. 

 General outline of the helmet and buckler combined elliptic-ovate, 

 their united length being nearly, but not quite, twice the maxi- 

 mum breadth of the buckler. Dorsomedian plate large, hexago- 

 nal, apparently rather wider than long ; its upper margin slightly 

 concave on both sides and somewhat pointed in the middle, its 

 lower margin being concave. Orbital cavity situated nearly in 

 the centre of the helmet, transversly reniform or bean-shaped in 

 outline, much wider than high. Upper margin of the orbital 

 cavity broadly, regularly and very shallowly concave, the lower 

 being correspondingly convex, while the two lateral extremities 

 are symmetrically and rather narrowly rounded. 



Pectoral spines extending nearly to the posterior end of the 

 buckler, thin and compressed vertically; moderately broad later- 

 ally where they are articulated to the ventro-lateral plate, and 

 widening to about their mid-length, where they exceed the breadth 

 at their articulation by about one line. From the widest point 

 the breadth of the spines is again gradually reduced up to the 

 joint separating the two segments of which they are composed, 

 from whence they taper gradually to an acute point. The two 

 segments are divided, nearly transversely, by a ball and socket 

 joint, the ball being in the anterior and the socket in the posterior 

 or terminal segment. The anterior end of each spine seems also 

 to be furnished with a ball and socket joint, as there is a strongly 

 inflected cavity in the ventro-lateral plate to receive the anterior 

 end of the spine which latter terminates in a rounded protuberance. 

 On the inner and outer lateral margin of the pectorals there is a 

 row of crowded, nearly erect, conical, tooth-like, hollow spines. 

 These are directed towards the articulation of the spine with the 

 ventro-lateral plate up to about the mid-length of the anterior 



