Reviews—Prof. K. v. Zittel’s Palichthyology. 127 
(not including the so-called A. falcifer) passes imperceptibly into 
Hybodus, so far as the dentition is concerned ; and in the two genera 
the dorsal fin-spines, head-spines, and shagreen are identical. Never- 
theless, Hybodus is the type of the “ Hybodontide”; Acrodus is by 
common consent admitted into the Cestraciontide. Already, the 
progress of research begins to suggest emendations. Ptychodus 
proves to have not the slightest affinity with the Cestracionts ;' and 
it is somewhat misleading to mention in connection with the teeth of 
this genus the large ribbed spines, which are afterwards correctly 
referred to Pelecopterus [= Protosphyrena | in the section on Ichthyo- 
dorulites, though truly pertaining to a Teleostean fish. 
The Scylliide and Scylliolamnide are not of much paleontological 
importance, but the succeeding Lamnidz and Carchariide naturally 
occupy a considerable space for full treatment. Doubt is rightly 
cast upon the supposed Carboniferous representatives of these families, 
and Sphenodus, of Jurassic age, is recorded as the earliest undoubted 
member of the Lamnide yet known. Meristodon is given as 
a synonym of Ozyrhina, but the type-specimens in the British 
Museum are fragments of Hybodont teeth; Otodus is retained, 
though with a reference to its suggested demolition by F. Noetling; 
and Coraa, as usual, is also placed in this family. In the description 
of Carcharodon, the omission to note C. longidens, Pillet,? is perhaps 
unfortunate, this tooth being supposed to occur in beds equivalent to 
the Maastrichtian, while all other undoubted representatives are 
Tertiary. On p. 83 Alopiopsis is misprinted Hopiopsis, and this ought 
to be placed as a synonym of Protogaleus, Molin (Sitzungsb. k. 
Akad. Wiss. Wien, vol. xl. 1860, p. 583). 
The Spinacide, with cyclospondylic vertebra, are next considered, 
and the Liassic Paleospinaxz holds its accustomed place as their 
earliest recognized representative. Quite lately, however, this fish 
has been found to possess an anal fin, and to have many vertebra 
feebly asterospondylic; and these characters, together with those of 
the teeth, remove it to a position among the Hybodonts.? The so- 
called Spinax primevus, from the Lebanon Chalk, is assigned to 
Centrophorus (after Hasse), and fragments of other genera and 
Species are recorded both from the Chalk and Tertiaries. But it is 
time that the Cretaceous ‘“‘Spinax major” were entirely omitted 
from lists, such smooth dorsal spines being indeterminable; and 
Egerton* and Hasse® have both shown that some, if not all, of the 
fossils in question are Cestraciont. 
The primitive family or group of Xenacanthide follows. The 
remarkable preservation of the Continental Permian specimens of 
Xenacanthus renders possible a somewhat detailed account of the 
hard parts of this genus, and thus throws considerable light upon 
1 Quart. Journ. Geol. Soc. vol. xliii. (1886), p. 121; Proc. Geol. Assoc. vol. x. 
(1888), p. 295. 
2 Mem. Acad. Sci. Savoie, [3] vol. ix. 1883, p. 277. 
3 Gout. Mae. [3] Vol. V. (1888), p. 499. 
4 Mem. Geol. Surv. Dec. xi. (1872), pl. ix. 
5 Neues Jahrb. 1883, vol. ii. p. 66. 
