224 
ANTI ARC IIA. 
Head and trunk broad, depressed, the scutes ornamented with 
tubercles partially or completely fused into a network of ridges; 
tail [if present] without dermal armature. Lateral sensory canals 
on the upper aspect of the head united by two transverse commis¬ 
sures arising from a point on the lateral plates, the anterior directly 
Fig. 34. 
Head of Bothriolepis canadensis, Whit.—Dorsal aspect, restored by R. H. Tra- 
quair. ay, angular ; e.l, extra-lateral (operculum) ; l, lateral; l.occ, lateral 
occipital ; m.occ, median occipital; p, postmedian; p.m, premedian. 
crossing the premedian, the posterior arched backwards, its right 
and left halves meeting in a sharp angulation upon the median 
occipital; anterior median dorsal plate overlapping the anterior 
dorso-lateral and overlapped by the posterior dorso-lateral, the two 
halves of a commissure arising from the lateral sensory canals on 
the posterior dorso-lateral plates meeting in an acute angle about 
the middle of its surface. Pectoral appendages at least as long as 
the armoured trunk, segmented into a distal and proximal portion, 
the latter being much larger than the former; marginal scutes of 
proximal portion meeting mesially, with a minute “ anconeal ” 
element only on the dorsal aspect; marginal and central scutes of 
distal portion more numerous than in Pterichthys. 
The form and arrangement of the bones occupying the orbital 
opening of this genus have been discovered and described in detail 
by Whiteaves \ The present writer has had the privilege of ex¬ 
amining the original specimens of the Canadian species elucidating 
the points made known, and is thus able to confirm all the deter¬ 
minations. The arrangement is very similar to that described above 
in Pterichthys (p. 210) ; but additional information as to the pre¬ 
cise form of the narrow, transversely-elongated plate in front of the 
pineal element is afforded thus :—“ The central portion of the little 
plate is continued downward at nearly a right angle, as a narrow 
1 Trans. Roy. Soc. Canada, vol. iv. sect. iv. (1887), p. 102, pi. vi. 
