*)8 THE CANADIAN NATURALIST. [Vol. X. 



by the different sliape of its post-dorsomedian plate, from 0, 

 cuspidatus by the different arrangement of the grooves on the 

 outer surface of its cranial shield, and from both by the peculiar 

 sculpture of its bony plates, 



Cephdlaspis Cainphelltonensis. Sp. Nov. 



Head shield (the only part known) large, somewhat pointed 

 in front, obliquely rounded at the sides anteriorly, and produced 

 behind into moderately elongated, slightly incurved cornua. 

 Maximum breadth about seven inches. Orbits varying in outline 

 from nearly circular to longitudinally broad ovate, sub-central, 

 approximated, placed at distances from each other varying in 

 different specimens from once to thrice the diameter of the orbit 

 itself. Antorbital prominences rounded-conical ; interorbital 

 prominence also conical but somewhat elongated longitudinally ; 

 postorbital valley bounded by two narrow raised ridges, each of 

 which starts from a prominence immediately behind the orbit : 

 about halfway between the orbits and the posterior margin these 

 ridges coalesce so as to form a single, broad and prominent but 

 somewhat obscurely defined, posterior ridge. 



Outer surface, which is very rarely preserved, polished and 

 almost smooth to the naked eye. When examined under a lens 

 it is seen to be minutely and densely pitted, the pits being very 

 irregular in their shape, size and method of arrangement. Where 

 the enamel is removed the surface is divided into numerous 

 well marked polygonal areas. 



Large fragments of the head-shield of this species are abund- 

 ant in the Campbellton breccia, but the most perfect specimens 

 yet obtained do not shew the outline of the posterior margin of 

 the shield at all clearly. The orbits and the prominences and 

 depressions in the central portion of the shield are often well de- 

 fined, but the specimens are always crushed and nearly always 

 exfoliated. Portions of the true outer layer of the test have been 

 seen only on the central portion of the outer margin of the sides 

 of one large fragment, and on the extremities of the cornua in 

 two or three other specimens. 



The genus Cephalasp)is has been divided by E. Ray Lankester 

 into three subgenera, viz., Eiiceplialaspis^ Htmicyclaspis and 

 Zenaspis, but as Hemic 1/ clasp is is stated to be devoid of cornua 

 it is clear that the C. CainpheUtonensis cannot belong to this 

 subgenus. Of the two which remain, Eucephalaspis and Zenas- 



