INTRODUCTION. 
Vll 
has practically cycloidal scales without peg-and-socket articulation. 
Moreover, while the endoskeletal supports of the dorsal and anal 
fins are in two series in such Palaeozoic genera as Elonichthys 
and Pygopterus , they are distinctly shown to he confined to one 
series in the Mesozoic Coccolepis. 
The last term of the Palaeoniscid series ( Coccolejns ) thus 
approaches a higher grade than that of the Chondrostei in the 
character of its dorsal and anal fins. In every other respect, 
however, it is typically and essentially Chondrostean; the baseosts 
of its pelvic fins are relatively as large and numerous as those of a 
modern sturgeon. It is noteworthy that the only known apprcxi* 
mation to a higher grade occurs among much more generalized 
fishes, those of the Triassic family of Catopteridae. 
The little that is known of Catopterus and Dictyojpyge , the two 
genera of Catopteridae, forms the subject of the opening pages of 
the present volume. Much of this information is unsatisfactory 
and needs verification ; hut it may be asserted, with considerable 
probability of correctness, that these fishes possess a Palaeoniscid 
head and shoulder-girdle, while the tail is only hemi-heterocercal, 
and the single series of supports in the dorsal and anal fins almost 
equals in number the apposed dermal rays. Such being the case, 
here is an interesting illustration of the common law, that the links 
between a lower and a higher group are not to be sought among 
the specialized types of the former but among those with the most 
generalized secondary characters. 
Palaeontology seems to demonstrate that the various modifications 
in the minor characters of the Palaeoniscid fishes eventually led to 
the development of a series of types which can only be described as 
extremely degenerate, namely the modern sturgeons (Acipenseridae) 
and paddle-fishes (Polyodontidae). 
There is much probability, indeed, that other degenerate series 
originated from Chondrosteans related to them ; and it is interesting 
in this connection to notice the case of the Belonorhynchidae 
(catalogued on pp. 9-23). These are eel-shaped fishes with a long 
pointed head, an abbreviate-diphycercal tail, short dorsal and anal 
fins, and small paired fins. The trunk is nearly always, if not 
always, destitute of ordinary scales ; but it is armoured with four 
distinct longitudinal series of imbricating scutes—one median 
dorsal, one median ventral, and a pair supporting the “ lateral 
line.” The dorsal and anal fin-supports are much fewer than their 
apposed rays, though apparently only in a single series ; and the 
