116 



Part III. — Twenty-fourth Annual Report 



V.— ON THE SPECIFIC CHARACTERS OF GADUS LUSGUS, 

 GAD US MJNUTUS, and GADUS ESMARK1L 



By H. Charles Williamson, M.A., D. Sc., Marine Laboratory, 



Aberdeen. 



(Plates V1IT.-X.) 



CONTEXTS. 



PAGE. 



Introduction, - - - - - . - 116 



List of Body-Dimensions, - - - - - 119 



List of Enumeration-Characters, ----- 121 



Discussion of the Averages, - 121 



The Numbers of Fin-rays, - - - - - - 124 



The Numbers of Vertebrae, - - - 129 



The Reproduction of the Three Species, - 130 



The Skulls of the Three Species, - - - - - 131 



A Discussion of the Species, - - - - - 133 



A Specific Description, ------ 135 



The Diagnosis of a Species, - - - 136 



General Appearance of the Three Species, - - - 136 



Key, 138 



Literature, - - - - - - - - 139 



List of Tables, - - - - 141 



Tables, - 142-158 



Introduction. 



The present research is a continuation of the paper contributed to the 

 Ticentie.th Annual Report of the Fishery Board for Scotland, Part III., 

 entitled, " A comparison between the cod (Gad us callarias), the saithe 

 (Gadus cirens), and the lythe (Gadus pollachius) in respect to certain 

 external and osteological characters." In that paper a beginning was 

 made with the review of the species of the genus Gadus. In several 

 instances the accepted specific descriptions are unsatisfactory ; so much so 

 is this the case that difficulty is experienced in separating certain species. 

 A certain amount of confusion has existed in the diagnosis of G. luscus 

 and G. minutus ; and the third species, G. esmarkii, which has, through 

 Dr. Fulton's trawling experiments, been shown to be common in Scottish 

 waters, might in its smaller stages be mistaken for a young minutus. The 

 three species under review are the three smallest species of the genus; 

 in the former paper the three largest members were dealt with. A 

 systematic study of the three forms has become necessary in order to 

 definitely fix the specific characters. It is very seldom that a single 

 member of a species will exhibit all the distinguishing characters well. 

 It has thus been necessary to examine a considerable number of specimens 

 of each species. The main purpose is to arrive at an accurate and suitable 

 specific description, and with this end in view T , both the characters in 

 which they agree, as well as those wherein they differ, must be studied. 

 A minute comparison is therefore instituted between the three forms, and 

 by the method which was adopted in the previous research. The method 

 has been to make a number of measurements on the body of the fish, in 

 order to determine the comparative magnitude of corresponding distances 



