4 A. S. Woodivard — Devonian Fishes, Canada. 



dimensions ; and one of these spines is shown of the natural size 

 in PI. I. Fig. 3. 



A. semistriaius pertains to the primitive section of the genus 

 (Mesacanthus of Traquair) already well known in the Lower 

 Devonian, but attains to at least twice as large a size as any of its 

 congeners hitherto discovered. 



OSTRACODERML 



Genus Cephalaspis, Agassiz. 

 [Poiss. Foss. vol. ii. pt. i. 1835, p. 135.] 



6. Cephalaspis campbelUonensis, Wliiteaves. PI. I. Fig. 6. 



1881-89. J. F. Whlteaves, Canadian Nat. n.s. vol. x. p. 98, and Trans. Roy. Soc. 



Canada, vol. vi. sect. iv. p. 92, pi. x. fig. 2. 

 1890. R. H. Traquair, Geol. Mag. [3] Vol. VII. p. 21. 



1890. Cephalaspis Whitenvesi, R. H. Traquair, ibid. p. 21. 



1891. A. S. Woodward, Catal. Foss. Fishes B. M. pt. iL p. 190, pi. ix. fig. 5. 



This is one of the commonest fishes in the Campbellton shale, but 

 the specimens are almost invariably so much crushed and broken 

 that the characters of the species are difficult to determine. The 

 latest definition, given in the British Museum "Catalogue," seems 

 to be correct ; and the examples of the head-shield in the new 

 collection display only two features worthy of special note. 



The most remarkable of these features — and one probably of much 

 significance — is the conspicuous difference between the structure of 

 the main part of the shield and that of the region termed the " post- 

 orbital valley." Whereas in shields that have lost the superficial 

 layer, the tesserae of the middle layer are well shown in every part 

 outside the " post-orbital valley," in this small area the tissue is 

 observed to be thickened and dense, with a splintery fracture, and 

 vrithout any sutures or conspicuous vascular canals. This hardened 

 plate, indeed, is so sharply separated from the surrounding shield, 

 that it has the appearance of an entirely independent element ; and 

 the writer is inclined to believe that some other Cephalaspidian 

 sliields in the British Museum, from the English Old Eed Sandstone, 

 exhibit characters capable of a similar interpretation. 



The tubercular nature of the superficial ornament of the shield 

 is also noteworthy. One specimen shows well-separated rounded 

 tubercles on the upper aspect of the cornua ; and the inferior rim 

 and rostrum of another specimen are marked with closely arranged, 

 flattened, irregularly stellate tubercles, sometimes almost fused into 

 a network. 



Finally, the new collection is interesting as comprising a single 

 specimen in which remains of the greater part of the squamation of 

 the trunk are preserved. The scales are unfortunately so much 

 crushed, broken, and displaced, that little of their arrangement can 

 be determined ; but their general appearance suggests that there 

 were fewer deep and narrow scales than in the typical species of 

 which the trunk is well known. Many of the scales are nearly 

 equilateral (PI. I. Fig. 6), and exhibit a very narrow overlapped 

 border. The hinder border is not serrated, but the unabraded 



