VI 
INTRODUCTION. 
wards enlarged the group by adding some extraneous genera (e. g. 
Lophius , Ostrcicion , and Syngnathus), and proposed the new term of 
Amphibia Nantes. Some years later, the Parisian Professor, de 
Lacepede 1 , returned to Artedi's conception of the Chondropterygii, 
or “ Poissons Cartilagineux,” as he preferred to term them; and 
the only author of note who has ventured to ignore such an arrange¬ 
ment is M. E. Bloch, whose ‘ Systema Ichthyologiae,’ edited by 
Schneider in 1801, comprises a series of orders based exclusively 
upon the number of the fins possessed by each fish, irrespective of 
the nature of the skeleton. 
In 1806, Constant Dumeril 2 , a pupil of de Lacepede, followed his 
teacher in dividing the Cartilaginous fishes into two groups, 
according to the presence or absence of an operculum ; and those 
possessing neither operculum nor opercular membrane were termed 
TREMATOPNks, and further separated into the two “ families ” of 
Cyclostomes and Plcigiostomes, according to the form of the mouth. 
The latter group comprised the Sharks ( iSquali ) and Bays ( Pnjce ) ; 
and, owing to the presence of an opercular membrane, the Chimse- 
roids were placed far apart, among the Chismopnes. 
In his well-known ‘ Begne Animal,’ Cuvier modified Dumeril’s 
family of Plagiostomes by adding the Chimseroids, and re-naming it 
Selachiens 3 ; and betwmen 1832 and 1841, Bonaparte 4 proposed to 
elevate this group into a subclass of Elasmobrancrii, the two 
subdivisions to be regarded as orders and known respectively as 
SelacJia (Sharks and Bays) and Holocepthcda (Chimaeroids). The 
Cyclostomes constituted a distinct subclass, that of Marsipo- 
branchii. About the same time, however, Agassiz 5 reunited these 
two subclasses under an order termed Placoidei, in reference to the 
character of the exoskeleton (when present)—a retrograde step in¬ 
duced by a too high estimation of palaeontological considerations. 
In 1846, Johannes Muller 6 adopted Bonaparte’s subclasses, 
though using the term “ Selachii ” as equivalent to Elasmobranchii, 
and naming the two orders, Plagiostomi and Holocephali. In 1861, 
Owen ' enumerated the Plagiostomi and Holocephali as distinct 
1 B. G. E. de Lacepede, Histoire Naturelle des Poissons, vol. i. (1798), p. 1. 
2 A. M. 0. Dumeril, Zoologie Analytique (1806), pp. 101-105. 
3 G. Cuvier, Begne Animal, vol. ii. (1817), p. 121. 
4 C. L. Bonaparte, Iconographica della Fauna Italica, vol. iii. (Pesci), 1832- 
41, Introduction. 
6 L. Agassiz, Becherclies sur les Poissons Fossiles, vol. i. p. 170. 
6 Abh. k. Akad. Wiss. Berlin, 1844 (1846), p. 203. 
1 B. Owen. Palaeontology (1861), pp. 99, 116. 
