448 CLASSIFICATION OF DEVONIAN FISHES 
to either of these orders is at present known in the fossil state ; that 
they are represented by a very small number of genera and species in 
our existing Fauna ; finally, that the Pharyngobranchii, from their very 
nature, could hardly be preserved in a recognizable state, even in such 
fine mud as that of the Oxford clay, or the Solenhofen slates, and that 
of the Marsipobranchii nothing but the horny teeth could be expected 
to escape destruction. Lepzdoszren, on the other hand, might have 
left as definite traces of its existence as Dzpterus, and hence its entire 
absence in the fossil state is a negative fact of greater value. 
3. The ELASMOBRANCHII abounded, teeth and spines testifying to 
the numerous and diverse genera which haunted the Devonian seas. 
It is more difficult to say to what sections of the order these genera 
belonged, as the only Devonian Elasmobranch whose whole structure 
can be restored with any certainty is Plewracanthus, a fish which be- 
longs to a family distinct from any now living. 
4. The GANOIDEI, as I have endeavoured to show above, are 
largely represented by a suborder, the Crossopterygide, which drops 
into comparative insignificance in later ages. Of the existence of 
Amiadz there is no evidence, and even if we include Tharszs, Thrissops, 
and Leptolepis under this suborder, they are scanty in all later form- 
ations ; but what is much more remarkable is the apparent, entire, or 
almost entire, absence of the Lepidosteidz, a suborder which obtains 
such a prodigious development in the Mesozoic epoch. The nature of 
the Acanthodide, and the question whether there is any reason to 
suspect the existence of Chondrostei during the Devonian epoch will 
be considered by-and-bye.! 
1 The determination of the characters of the families of Lepidosteidze and of the limits of 
the suborder is a difficult problem, of which I hope to treat more fully hereafter. One 
interesting fact results from my investigations, so far as they have hitherto gone, viz., that 
Lepidosteus belongs to a totally distinct family from its Mesozoic allies, whether ‘* Sauroids” 
or ** Lepidoids.” The Pycnodonts and Hoplopleuride do not appear tome to belong to the 
Lepidosteide, and I doubt their being true Ganoids. For the present I propose the following 
as a sketch of an arrangement of the Lepidosteidz. 
LEPIDOSTEID-. 
Heterocercal Ganoids with rhomboidal scales ; branchiostegal rays ; non-lobate paired 
fins ; a preoperculum and an interoperculum. 
Fam. 1. Lepidosteini. 
Maxilla divided into many pieces; branchiostegal rays few and not enamelled. 
Lepidosteis. 
Fam. 2. Lepidotini. 
Maxilla in one piece; branchiostegal rays many and enamelled; the anterior ones 
taking the form of broad plates. 
(a) Bchmodus, Tetragonolepis, Dapedius, Lepidotus, &c. 
(b) Lugnathus, Pachycormus, Oxygnathus, &e. 
(c) Asprdorhynchus. 
Perhaps the genera marked a, b, v, should form distinct sub-families. 
