introduction. 
VII 
orders of a subclass, though only allowing the difference to rank of 
equal importance with that observed between the Acanthopterygian 
and Anacanth Teleosteans. 
In 1870, Dr. Giinther 1 once more adopted Bonaparte’s classifica¬ 
tion, altering the nomenclature, however, and terming the sub¬ 
classes Chondropterygii and Cyclostomata respectively, and the 
orders of the former, Plcigiostomata and Holocejphala ; while the 
Plagiostomes were further divided into the suborders of Selachoidei 
and Batoidei. A year later 2 , the Chondropterygii, thus defined, 
became an order of Dr. Giinther’s newly instituted subclass Pal.e- 
ichthyes, the Plagiostomata and Holoc-ephala then being suborders, 
and the Selachoidei and Batoidei merely sections. 
At the same time, Prof. Cope 3 proposed a precisely reverse modi¬ 
fication, the Sharks and Bays to form one subclass (Selachi) and 
the Chimaeras another (Holocephali) ; this arrangement being 
based upon the fundamental difference in the structure of the skull, 
already indicated in Bonaparte’s second term. In 1876, Prof. 
Huxley 4 adopted Cope’s wide separation of these two groups, but 
regarded them as orders, and preferred the term Plagiostomi to that 
of Selachi. Host modern researches have also tended to emphasize 
the distinction between fishes with autostvlic % and those with hyo- 
stylic 6 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, it will be observed that the signi¬ 
ficance of each name already adopted has considerably varied accord¬ 
ing to the views of the respective authors. The only term originally 
restricted to the cartilaginous hvostvlic fishes is that of “ Plagrio- 
stomi,” proposed by C. Dumeril; but this is both inappropriate in 
many instances, and also based upon a misconception of the sup¬ 
posed relationships existing between the lampreys and the sharks. 
We therefore venture to follow Prof. Cope in adopting Bonaparte's 
name, Elasmobranchii, excluding the Holocephali, and elevating 
these to the rank of an equivalent subclass. 
In subdividing the Elasmobranchii, thus defined, almost all natu- 
1 A. C. L. G. Gunther, Catalogue of the Pishes in the British Museum, 
vol. viii. (1870), pp. 348, 353, 499. 
2 Phil. Trans. 1871, p. 554. 
3 E. D. Cope, Proc. Amer. Assoc. Adv. Sci. 1871, p. 326. 
4 H. T. Huxley, Proc. Zool. Soc. 1876, p. 57. 
8 1. e., skull without separate suspensorium. 
e I. e., skull with separate suspensorium. 
