74 . Reviews—JI. W. Davis—Fossil Fishes. 
pectoral fin, and a few neural or hemal arches and fin-supports are 
referred to; but the only skeletal elements of importance are por- 
tions of cartilage. There are some beautiful figures of the more or 
less fragmentary jaws; and many other pieces of calcified cartilage of 
varying shape are both described and figured. Mr. Davis’s main 
contention is, that many of the cartilages show a distinct segmenta- 
tion—a feature observed by Cope in the Pleuracanth skulls from 
Texas; and certainly, it must be admitted, some of the fossils 
present appearances rather suggestive in this connection. More 
satisfactory specimens, however, are still required before any definite 
result can be arrived at; and whether or not Mr. Dinning’s fossil, 
for example (pl. Ixvii. fig. 2), be the cranial roof of a Pleuracanth, 
the restored sketch (ibid. fig. 2a.) appears to usto be unjustifiable 
imagination totally at variance with the most fundamental principles 
of Elasmobranch anatomy. We are disposed to criticise, too, when 
clavicular elements are ascribed to the shoulder-girdle (p. 711); and 
there is a distinct contradiction in regard to shagreen, this being 
said to be absent in Pleuracanthus on p. 705, while “masses of 
shagreen” are described as found with remains of this genus on 
p- 714. Some of the species must have attained a very large size, 
one slab of jaws from Newsham probably indicating a fish between 
3 and 4 metres in length. 
The systematic portion of the work, as we have said, relates 
chiefly to spines, and the following species are recognized :— 
Pleuracanthus levissimus, Ag. Pleuracanthus obtusus, nom. nov. 
robustus, Davis. (=Phricacanthus biserialis, Davis). 
Wardi, Davis. serratus, Sp. Nov. 
undulatus, sp. NOV. Woodwardi, sp. nov. 
tenuis, Davis. (Lophacanthus) Taylori, Stock. 
denticulatus, Davis. (Compsacanthus) triangularis, 
Howsei, sp. noy. Davis. 
alatus, Davis. — (Diplodus) equilateralis, Ward. 
erectus, Davis. [A tooth. | 
horridulus, Traquair. Anodontacanthus acutus, Davis. 
TL 
cylindricus (Ag.) Davis. obtusus, Davis. 
Thomsoni, sp. nov. 
All these spines are described in detail, with their ascertained 
distribution, and each description is accompanied by one or more 
fine figures. The specific characters are chiefly found in the shape 
of the transverse section, and in the form and situation of the denti- 
cles. Only a very small amount of variation is allowed in each case, 
while several new forms of spine are named ; and it must remain 
for future discoveries of complete fishes to determine how far these 
observed differer ces are of specific value. We would only remark 
that it is somewhat hazardous to identify two Lower Carboniferous 
spines (as the author does) with species characteristic of the Upper 
Carboniferous; and we are inclined to think that some of the 
differences in denticulation will prove to be due entirely to 
chemical erosion dur‘ng fossilisation. 
The fragmentary nature of the fossils described admits of so much 
difference of opinion in many determinations, that it scarcely seems 
profitable without further evidence to discuss the various points. 
