BIOGRAPHICAL METHOD 51 



7. The interorbital width is, in most cases, the distance between the inner margins 

 of the eye-balls. Where the eyes are separated by a flat or concave space bounded 

 by a pair of sharp ridges forming the inner edges of the orbits the distance between 

 these ridges is measured. 



8. In indicating the size of the mouth the position of the hinder edge of the 

 maxillary in relation to the lower eye is given. By the length of maxillary is meant 

 the total length of the upper jaw, measured from the extremity of the snout, and this 

 includes the praemaxillary as well as the maxillary itself. Unless otherwise stated, 

 the jaws are measured on the ocular side of the head. 



g. By dental formula — ~ = ^-- it is understood that there are 4 teeth on 



■^ ■' 2 — 3+12 — 16 



the ocular side of the upper jaw and 13 to 15 on the blind side : in the lower jaw- 

 there are 2 or 3 teeth on the ocular side and 12 to 1 6 on the blind side. 



10. The size of the scales is not indicated by means of a formula, as this not 

 infrequently leads to confusion. The number of scales in the lateral line is generally 

 counted just above the line itself, from a point opposite the upper angle of the gill- 

 opening to the base of the caudal fin. In those species in which the scales are easily 

 rubbed off it is sometimes necessary to count those in the lateral line itself. Where 

 the number of pores in the lateral line is less than the number of scales, this fact is 

 usually indicated The number of scales in a transverse series between the lateral 

 line and the middle of the back is counted in an oblique row. 



By caudal peduncle twice as deep as long is meant that the least depth of the 

 muscular part of the tail is twice as great as its length, which is measured from opposite 

 the last rays of the dorsal and anal fins to the posterior part of the peduncle ; the 

 length does not include the basal part of the caudal fin itself, which may be covered 

 with scales. 



X. BIBLIOGR.\PHICAL METHOD. 



In preparing the synonymy of each species an attempt has been made throughout 

 to limit this as far as possible, by including only the essential references. Thus, all 

 quotations from purely popular works and manuscript names ha\'e been excluded.^ 

 Extracts from purely nominal lists ha\-e usually been omitted, especially where the 

 species in question is from a region covered by earUer references, as have references to 

 descriptions, etc., copied verbatim from earlier authors and accompanied by copies 

 of original figures. In general, the papers cited in each synonymy are those which 

 have some bearing on taxonomy, or which extend or alter the known distribution of 

 the species. In doubtful cases I have erred on the side of liberality, and included a 

 number of references at the expense of the length of the bibliography. In cases 

 where the de\elopment of the species has been investigated, a list of the more impor- 

 tant papers dealing with the eggs, larva; and young has been added below the main 

 synonymy. 



In the case of current journals, etc., the abbreviations used are, for the most part, 

 those adopted by the compilers of the ' Zoological Record '. For the earlier works, 

 the abbreviations used by Sherbom in his ' Index Animalium ' have been followed. - 

 With very few exceptions, every reference has been taken from the original work 

 and has been checked by myself. 



^ Papers in Japanese and Russian, unprovided with an abstract, have usually been omitted 

 unless of special importance. 



- I take this opportunity of expressing my sincere appreciation of the valuable help provided 

 by the ' Index Animalium ', which has not only greatly lessened the risks of omission, but has 

 considerably lightened the labour of preparing the synonymies. My best thanks are due to Dr. 

 C. Davies Sherborn for frequent help and advice on matters nomenclatorial freely given during the 

 preparation of this monograph. 



