PALZEONISCI DiE. 
427 
It is not certain whether any narrow chain of supratemporal 
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 (cl) having a 
short inferior limb, and being bounded in front by a small 
triangular infraclavicle (i.d) ; 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. 
