368 Reviews—British Museum Catalogues— 
as Selacha (Sharks and Rays) and Holocephala (Chimeroids) ;” and 
the Cyclostomes to constitute a distinct subclass. Agassiz about the 
same time ‘“‘reunited these two subclasses under an order termed 
Placoidei.” ‘In 1846 J. Miller adopted Bonaparte’s subclasses, 
though using the term Selachii as equivalent to Elasmobranchii, and 
naming the two orders, Plagiostomi and Holocephali.” Bonaparte’s 
classification was also adopted in 1870 by Dr. Giinther, but he 
termed ‘the subclasses Chondropterygii and Cyclostomata re- 
spectively, and the orders of the former Plagiostomata and Holo- 
cephala; while the Plagiostomes were further divided into the 
suborders of Selachoidei and Batoidei.” But in 1871 Dr. Gunther 
instituted his subclass PaLmicuruyns, of which the Chondropterygii 
- became an order, and Plagiostomata and Holocephala were reduced 
to suborders. In the same year Prof. Cope proposed to unite the 
Sharks and Rays in one subclass (Sunacuz) and the Chimeeras to 
form another (Honocrruatt) ; “this arrangement being based upon 
the fundamental difference in the structure of the skull already 
indicated in Bonaparte’s second term.” ‘This classification was 
accepted by Prof. Huxley in 1876, but he regarded the two groups 
as orders, “and preferred the term Plagiostomi to that of Selachi.” 
Our author also adopts Cope’s classification, and adds, “Most modern 
researches have also tended to emphasize the distinction between 
fishes with autostylic, and those with hyostylic skulls, both among 
those without membrane-bones and those possessing these skeletal _ 
elements ; and such is the arrangement selected for adoption on the 
present occasion.” 
“With regard to terminology,” the author observes, ‘‘the only 
term originally restricted to the cartilaginous hyostylic fishes is that 
of ‘Plagiostomi,’ proposed by C. Duméril; but this is both inappro- 
priate in many instances, and also based upon a misconception of 
the supposed relationship existing between the Lampreys and the 
Sharks. We therefore venture to follow Prof. Cope in adopting 
Bonaparte’s name, Hlasmobranchii, excluding the Holocephali, and 
elevating these to the rank of an equivalent subclass.” 
Prof. Cope, in 1884, established a new order of the Hlasmobranch 
subclass, based upon his studies of some fish remains from the 
Permian beds of Texas, possessing teeth of the Diplodus type, and 
also exhibiting ‘an arrangement of the mandibular and hyoid arches 
extremely similar to that observed in the living Notidanus.” ‘There 
are other supposed distinctive structural characters of the cranial 
elements; and upon these fossils Prof. Cope founds his genus 
Didymodus, to be included with Pleuracanthus and the Hybodontidee 
in an order he terms JoHTHyYorTomt. 
The necessity for forming a new order for the reception of Pleura- 
canthus has also recently (1888) been remarked by M. Charles 
Brongniart, who has been able to study numerous specimens of 
the genus, in fair preservation, obtained from the Middle Coal- 
measures of France. The evidence thus attained enables him to 
attempt the restoration of the entire skeletal structure of the fish ; 
and to suggest inclusion in a new order which he proposes to term 
“« Pleuracanthides.” 
