XIV 
INTRODUCTION. 
dontidse bear much the same relation to the Permian Acentrojphorus 
as the modern sturgeons to the Palaeozoic Palaeoniscidae; the latter 
having only advanced a stage further in the matter of teeth, which 
are in them not only destitute of successors, but are also lost before 
the fish becomes adult. Among Pycnodontidae as a race, tooth- 
specialization consists in the reduction of the tritors into a few 
regular longitudinal series, and there is only one known genus (the 
Cretaceous Anomoeodus) in which there is much tendency towards 
the loss of this armature. 
The facts detailed in the Catalogue, as just briefly analysed, seem 
to render it unnecessary to discuss the still widely prevalent belief 
that the Pycnodonts are the direct successors of the Platysomidae. 
The elaborate researches and careful reasoning of Traquair sixteen 
years ago, 1 ought to have sufficed ere this to banish the theory even 
from popular handbooks; nevertheless, it survives in a shape 
scarcely different from that current at the time when comparatively 
nothing was known of the Platysomid skeleton. It must suffice to 
repeat, that the Platysomidae never make the faintest approach to 
the Pycnodontidae in a single essential character. The trunk and 
fins are as thoroughly Chondrostean in the most specialized as in 
the most generalized type; the cranial osteology and arrangement 
of the jaws are fundamentally different even when the dentition is 
most powerful. 
If speculation were permitted in seeking for the direct ancestors 
of the Pycnodonts, it might be most profitable to turn towards the 
earliest Mesozoic fishes of the Colobodus-tyipe. The appearance of 
the family, however, still remains as mysterious as that of the 
Coelacanthidse among the Crossopterygians; and the long-continued 
permanence of so remarkably specialized a type (Lower Lias—Eocene) 
is curiously paralleled in the range of the more primitive family 
just mentioned (Lower Carboniferous—Chalk). Persistent types of 
this character are rarely met with. 
Eugnathidce. 
It has already been mentioned that the small-mouthed Proto- 
spondyli considered above appear to have left no descendants. 
At least, no definite links can be recognized between these and 
modern fishes. The large-mouthed Protospondyli with conical 
teeth, on the other hand, can be traced from the Trias upwards 
1 E. H. Traquair, “ On the Structure and Affinities of the Platysomidce,” 
Trans. Eoy. Soc. Edinb. vol. xxix. pp. 343-391, pis. iii.-vi. (1879). 
