THE DEVONIAN EOCKS OF CANADA. 



93 



The gentis Cephalas/ns has been divided by E. Ray Lankester into three subgenera, 

 viz., Eucephalaspis, Hemicydaspis and Zenaspis, but as Hemicydaspis is stated to be devoid of 

 corniia it is clear that the C. Cambelltonensis cannot belong to this si\bgentis. Of the two 

 which remain, Eucephalaspis and Zenaspis have precisely similar head-shields, but the 

 body of Zenaspis has a dorsal sciite placed immediately behind the posterior spine. In 

 the absence of any knowledge of the body of the Campbellton species, therefore, it is 

 iincertain to which of these two subgenera it should be referred. 



Including the C. Dawsoni of Lankester, from Gaspé, all the specimens of Cephulaspis 

 hitherto described, are said to l>e characterized by a surface ornamented by raised tuber- 

 cles, so that the C. Cambelltonensis may be readily distinguished by its minutely pitted 

 sculpture. In general outline, the head-shield of the present species appears to be very 

 much like that of the Eucephalaspis Powriei from the Old Red Sandstone of Forfarshire. 



CoccosTEUS AcADiciTS, Whiteaves. 

 (Plate IX.) 



Coccosteus Acadicus, "Whiteaves, 1881. Can. Nat. and Quart. Jouru. Sc, N. S., Vol. X, p. 94. 



Cranial-shield (Woodcut and Plate IX, fig. 1.) — Flattened or depressed centrally and a 

 little in advance of the centre, but always rising into a broad, low prominence on the 

 median line at a short distance from the posterior margin ; sides somewhat sloping. 

 General outline that of an ovoid truncated at its broadest extremity, the truncation being 

 posterior, the length and breadth nearly equal, and the greatest breadth behind the mid- 

 length. Postero-lateral angles {a.a.) somewhat produced ; lateral margins most convex 



a. a 



Fig. 2. — Outline of a specimen of the cranial shield of C Acadicus, shewing 



the rostral plate (c) in situ. Some of the superficial grooves 



restored from other specimens. Natural size. 



