﻿PAL^ONISCTDiE. 427 



It is not certain whether any narrow chain of suprateraporal 

 plates (fig. 54, s.t) is present behind the cranial shield ; but there is 

 a very large post-temporal (p.t) on each side, above the operculum 

 and pectoral arch. The membrane-bones of the latter are all 

 conspicuous and externally ornamented ; the clavicle (d) having a 

 short inferior limb, and being bounded in front by a small 

 triangular infraclavicle (i.cl) ; the supraclavicle (s.cl) deep and 

 narrow, traversed above by the " lateral line," and bounded behind 

 at its articulation with the clavicle by a small postclavicle (p.cl). 

 Nothing is known of the scapulo-coracoid cartilage, but a small series 

 of radials is sometimes seen at the base of the pectoral fin-rays. The 

 basipterygium (axonost) of the pelvic fin has not yet been observed in 

 any genus, probably on account of non-ossification ; but the radial 

 cartilages (baseosts) form a well-developed series of elongated ele- 

 ments in Coccolepis australis, and it is probable that thisis a common 

 feature of the family. The dermal rays in all the fins are, as a 

 rule, delicate, articulated, and bifurcated distally ; a few genera 

 only exhibiting simple rays, and some others having rays without 

 articulation in the pectoral fin. In the median fins, the endoskeletal 

 supports are always less numerous than the dermal rays, and they 

 never appear to overlap the neural spines of the axial skeleton 

 beneath. 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, and 

 the distal of stout baseosts ; but in the Jurassic Coccolepis the 

 baseost series seems to have completely disappeared. The dermal 

 rays are to a slight extent imbricating, and the stouter portions are 

 ordinarily coated more or less with ganoine. 



The scales are typically rhombic, and united on the flanks by a 

 peg-and-socket articulation ; but in some genera (e. g., Cryphiolepis 

 and Coccolepis) the overlap of the successive series is so extensive 

 that they become essentially cycloidal, and the internal rib, with 

 its articular facettes, disappears. All the scales are more or less 

 coated with superficial ganoine, and the course of the lateral line is 

 marked by a series of perforations, which terminate at the base of 

 the upper caudal lobe. There is a dorsal and ventral series of 

 azygous ridge-scales which are often enlarged, especially at the 

 bases of the fins and upon the superior caudal lobe ; and these are 

 ordinarily continued by fulcra on the front margin of the fins. It is 

 also worthy of note that the downward and backward trend of the 

 scales is suddenly reversed at the base of the upper caudal lobe ; 

 and even when all the other scales are rudimentary or absent, 

 the squamation of this lobe is always robust. 



