424 Reviews—C. Brongniart—On Pleuracanthus. 
immediately behind, sharply separated from the upper half of the 
elongated diphycercal caudal, to the commencement of which. it 
extends. But most singular and novel are the two small repre- 
sentatives of the anal fin, which are “placed one behind the other 
and have the appearance of true limbs. Narrow at their base, they 
enlarge mesially, and then become contracted. Their skeletal 
framework is almost identical. The hemapophyses supporting 
them are truncated instead of ending in a point. The first two 
hemapophyses bear very slender interspinous elements which are 
in connection each with a fin-ray. The third is larger, broad at its 
extremities, supporting distally a shorter broader ossicle. From 
this are detached, above a ray, and below two short ossicles, of 
which the first supports an ossicle and fin-ray, and the second two 
ossicles and two fin-rays. We find nothing comparable in nature, 
fossil or recent.” It may also be added that Dr. Anton Fritsch 
will be able to make known interesting confirmatory—perhaps 
supplementary—evidence upon these points, when the Bohemian 
Pleuracanths are described, the writer of the present notice having 
been favoured with an inspection of beautiful examples in Prague. 
The completed memoir on this important discovery has yet to 
appear, but M. Brongniart remarks, at the conclusion of the pre- 
liminary note, that, as the result of his studies, Plewracanthus must 
be regarded as representing at least a distinct order, perhaps a sub-class, 
the * Pleuracanthides,”—“ a group ancestral to, and connecting, the 
Dog-fishes, Cestracionts, Rays, Chimeras, Sturgeons, and Ceratodus.” 
It is to be hoped, however, that before proposing any new term, the 
author will consider in more detail the conclusions of previous 
workers in the same direction. Prof. Cope has already placed a 
member of the group in a distinct order, the “Ichthyotomi,” 
equivalent in value to the order of Selachii; and although Mr. 
Garman remarks, apparently with much reason, that the definition 
originally proposed (relating to so-called distinct traces of ossification 
in the chondrocranium) is very doubtfully accurate, all recent 
researches have tended towards as complete an isolation of the 
Pleuracanthus-like fishes as now seems inevitable. Dr. Traquair’s 
description of the genus Chondrenchelys, with the appearance of a 
splint-like bone (? parasphenoid) upon the chondrocranium, and with 
complete broad vertebral rings in the caudal region, will likewise 
require consideration ; and the same author’s discovery of a uniserial 
archipterygial pectoral fin in Cladodus seems to the writer of this 
notice to place that much-discussed genus also in the great 
Pleuracanth order. The archipterygial character of the pectoral fin 
will certainly become one point in the broad diagnosis of the group, 
although, it must be admitted, a few Selachii (e.g. Squatina) exhibit 
some faint approach to that condition ; and it cannot be said that the 
torm of the teeth will count of much value, for the depressed and 
posteriorly expanded character of the base in the teeth of Cladodus 
is precisely paralleled in some Notidanidee and undoubted Hybodonts, 
which are true Selachii. It has hitherto been too much the custom 
to regard every ancient fish, destitute of membrane bones and 
