846 The American Naturalist. - [September, 
allied to Rhizodus. Important discussions of the characteristics of 
the best-known Paleozoic genera are entered on, especially of Macrop- 
etalichthys, Onychodus, Bothriolepis, Dinichthys, Titanichthys, My- 
lostoma, and Edestus 
In the discussion of the affinities of these and other genera, the zool- 
ogist who has gone beyond the views held in the days of the elder 
Agassiz will find a good deal to criticise. In fact, modern taxonomic 
views do not seem to have taken much hold on the mind of Professor 
Newberry up to the time of writing this book. The principal source 
of error is the tendency to compare the extinct with very different 
recent forms, to which they may have some superficial resemblance. 
This is a oy BB möre praiseworthy than the opposite extreme 
that p ts—that is, the habit of neglecting exist- 
ing fonan as though all of ihe latter have originated in modern times, 
which we well know is not the case. However,when Prof. Newberry com- 
pares Macropetalicthys with the sturgeons, he is certainly wide of the 
mark. This genus is a Placoderm, allied to Homosteus, and the areas 
on the cranium indicated by Prof. Newberry as separate elements, 
comparable to those of the true fishes and Batrachia, are not such, 
but are merely the.spaces inclosed by the tubes of the lateral line sys- 
tem. (See Fig. 2, p. 43.) The true cranial segments are different, 
as I hope soon to show. As to the D:nichthyida, Professor Newberry 
follows Huxley in referring them, and of course other Placodermi, to 
the neighborhood of the Nematognathi of modern waters. Since the 
discovery of the dorsal fin in Coccosteus by von Koenen and Traquair, 
it is evident that the resemblance to the Siluroids is scarcely even 
superficial. In describing Coelosteus, Prof. Newberry regards it as 
allied to Pappicthys, and the order of the Halecomorphi; but this 
cannot be accepted, as the character of the ossification is that of vari- 
ous truly Paleozoic types, and the general characters approach espe- 
cially to Rhizodus. 
n commenting on Macropetalichthys, the author asserts that the 
absence of lower jaw need not be regarded as a character of much 
importance, as is done by Haeckel and others. In this zoologists will 
probably agree with Professor Haeckel, and will make the systematic 
inferences from it which it warrants in the case of the Pteraspididze, 
for example. 
 . In his conclusion that the remarkable structures to which the name 
Edestus has been applied are median dorsal procumbent spines, ichthy- 
, ologists will agree that Prof. Newberry has given the most plausible of 
all the attempted explanations yet offered. 
Ld 
