CLASSIFICATION. lxxix 



CLASSIFICATION. 



As to the system followed in this work I have simply accepted, so far as 

 I possibly could, that employed in the British Museum Catalogue, as 

 specimens are arranged in the National Collection in accordauce with it. At 

 the present time Ichthyologists may be considered as engaged in sto ring-up 

 facts from which after a longer or shorter interval a general system will have 

 to be evolved. Whether therefore one commences with the spiny-rayed 

 teleostean perches, or begins from the higher and more specialized groups 

 of sharks and their allies, seems to be a matter of trivial importance. 



The following is the classification adopted : 



Sub-class, I Teleostei -< 



'Order 1. Acanthopterygii, vol. i, p. 1. 



2. Anacanthini, i, p. 271. 



3. Physostomi, ii, p. 46. 



4. Lophobranchii, ii, p. 256. 



5. Plectognathi, ii, p. 267. 



, . TT _, r Order 1. Ganoidei, n,'p. 278. 



feub-class, 11 Uhondropterygii ! _ _,. . ..... or 



C ,, 2. Elasmobranchn, n, p. 285. 



Snb-class, III Cyclostomata, ii, p. 355. 



Sub-class, IV Leptocardii, ii, p. 366. 



Although it is easy to refer to Families as groups of Genera and the 

 latter as an assemblage of species, this merely brings us to the real question 

 at issue, which is, what is a species ? For determining this two lines of 

 investigation may be followed : (1) the morphological or that which relates to 

 structure and development, or wherein individuals agree one with another 

 but differ from other fishes ; and (2) the 'physiological or such as pertain to 

 function, as whether the forms under consideration are normally capable of 

 fertile union one with another (but not so with those of other groups) , being all 

 descendants of a primitive race of ancestors. A variety is one which differs 

 in some characters from the type of the species, but between which a distinct 

 intermediate gradation has been observed. While a local race may be also a 

 variety but wherein no such connecting chain has yet been discovered. What 

 some consider a variety others would deem a local race or sub-species; thus 

 a permanence of variation has been held to constitute a species, but its 

 instability a variety. 



Irrespective of the foregoing there are other forms of variation ; thus 

 larval fish as the Leptocephalus (vol. ii, page 239), or young of the conger 

 and some other fishes, may have their development arrested, in which 

 condition they may still live for a longer or shorter period. Monstrosities are 

 generally the result of some abnormal condition of the embryo, sometimes 



