84 PISCES. 



seen in arched series, while a small median gular plate covers 

 the space where the two sides meet in the front angle of the 

 mandible. There is as yet no definite evidence of ossifications in 

 the sheath of the notochord, and ribs are always wanting. In 

 the Jurassic genus Coccolepis, the neural spines are not fused 

 with the supporting arches in the abdominal region, but both 

 these and the haemal spines are firmly fixed to their arches in 

 the tail. At the base of the caudal fin the heemals are much 

 enlarged for the direct support of the dermal rays, while the 

 neurals become gradually aborted, and there is a series of 

 distinct supporting ossicles beneath the fulcra of the upper 

 caudal lobe. The pectoral arch comprises clavicle, infraclavicle, 

 supraclavicle, and one postclavicle, while a very large post- 

 temporal plate connects it with the skull. In Coccolepis the 

 considerably extended pelvic fins have their rays directly 



'supported by a series of elongated baseosts ; but the axonost 

 has not hitherto been observed in any genus. There is a single 

 dorsal and anal fin, with the rays less numerous than their 

 endoskeletal supports; and in some of the earlier types (e.g., 

 Elonichthys and Pygopterus) these supports are distinctly 

 shown in the dorsal fin to be arranged in two series the 

 proximal of slender axonosts, the distal of stout baseosts while 

 in Coccolepis the baseost series seems to have completely dis- 

 appeared. The scales are typically rhombic and united on the 



' flanks by a peg-and-socket articulation ; but in some genera 

 (e.g., Crypliiolepis and Coccolepis} they are essentially cycloidal, 

 deeply overlapping and without articulation. The ridge-scales 

 on the upper caudal lobe are much enlarged. 



Cheirolepis (fig. 62). A genus remarkable for the very small size of 

 the scales, which are strengthened on the inner face by a vertical ridge, 

 ' but scarcely overlap. The branchiostegal rays of the foremost pair are 

 much larger than the regular series behind. All the fins are fringed with 

 conspicuous fulcra, intercalated between the tips of the foremost gradually 

 lengthening rays ; and the ridge-scales of the upper caudal lobe are 

 divided into two halves at the apex. The pelvic fins have a much- 

 extended base, and the dorsal fin is even more remote than the anal. The 

 typical species, C. trailli (with many synonyms), occurs in the Old Eed 

 Sandstone of N. Scotland, and another well-preserved form, C. canadensis, 

 has been found in the Upper Devonian of the Province of Quebec, Canada. 



