J. F. Whiteaves—New Species of Ptericthys. 135 
ornata shall have been described and figured, it will be impos- 
sible to institute an accurate comparison between it and the 
nearly related Canadian form. There are, however, good rea- 
sons for supposing that the European species attained a much 
larger size than the Canadian, for Agassiz says that the 
plates of B. ornata are from three to six inches in length, 
and, judging by this, the approximate length of its helmet 
and buckler together may be roughly estimated at from six 
Under the circumstances, the writer thinks it most prudent 
to give to the Canadian Péericthys a local and provisional name, 
with a brief diagnosis of its most salient characters, as follows: 
premising that a more detailed description of the species, accqm- 
panied with figures, will appear at an early date in one of the 
publications of the Canadian Geological Survey. 
Prericruys (Bornriotepis) CanapEnsts, Nov. Sp.—Plastron 
nearly flat. Helmet moderately arched above, most prominent im- 
mediately 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. Buckler 
slightly arched, median keel strongest in the center of the dorso- 
median plate, and in the posterior half of the post-dorsomedian. 
General outline of the helmet and buckler combined elliptic-ovate, 
their united length being Rae 4 but not quite, twice the maxi- 
concave on both sides and somewhat pointed in the middle, its 
lower margin being concave. Orbital cavity situated nearly in the 
center of the helmet, transversely reniform or bean-shaped in out- 
line, much wider than high. Upper margin of the orbital cavity 
broadly, regularly and very shallowly concave, the lower bein 
correspondingly convex, while the two lateral extremities are 
symmetrically and rather narrowly rounded. 
ectoral spines extending nearly to the posterior end of the 
buckler, thin and compressed vertically; moderately broad laterally 
where they are articulated to the ventro-lateral plate, and widen- 
1ey an The two 
segments are divided, nearly transversely, by a ball and socket 
