of the Fishery Board for Scotland. 



121 



greater accuracy to be obtained on the whole by making the measure- 

 ments on such a board as described in the 18th fteport, than by merely 

 stepping off the distances on the fish with a pair of dividers. If the fish 

 are in good condition, in both methods greater accuracy will be obtain- 

 able than in specially soft specimens. 



The measurements were made in centimetres. 



The Measurements Represented as Percentages of one Common 

 Standard. — All the body dimensions were converted into percentages of 

 one standard, viz., the length of the fish. 



The Length of the Fish is the distance from the anterior tip 

 (premaxilla or mandible, as the case may be) to the end of the middle 

 rays of the tail fin. 



The fishes of each species have been arranged in centimetre groups. 

 The average of the percentages of the length of the fish which each body 

 dimension was found to represent was calculated for the fishes of each 

 size. They have been arranged in Tables VII, VIII, IX, X, XI, XII. 

 Alongside each average is added in brackets the number of fishes on 

 which the average is based. 



The average percentage for each character has then been calculated in 

 all the fishes of each species in which the character was noted. The 

 number of characters examined in each specimen varied very much; 

 while in some all the characters were noted, in others one or two 

 characters were measured. 



Enumeration- Characters. 



The Number of Kays in the Unpaired Fins. — The enumeration 

 of the fin-rays is rendered difficult from the fact thst we are dealing with 

 small fishes. The last rays in the fins with the exception of the first 

 dorsal are minute. The first rays of the first anal fin are sometimes 

 liable to be missed on account of their very small size. 



In a few cases the number of rays in the paired fins and the caudal fin 

 was counted. 



The Number of Vertebra. — The number of vertebrae was counted 

 after the fish had been boiled. The posterior vertebras are very small ; 

 the backbone tapers down to a fine extremity. The vertebrae are not so 

 easily counted in preserved fishes as in fresh specimens. A fish that has 

 been preserved in formaline solution, when boiled, usually becomes 

 distorted. This is due to unequal shrinkage ; the skin is much affected 

 in this respect, becoming very tough. The vertebra bearing the ural 

 elements is counted as the last vertebra. 



The Number of the Vertebra Bearing the First H^mai, 

 Arch. — This character was noted in a number of instances. 



Discussion of the Body Dimensions. 



The averages taken along with the range of variation of the character 

 gives a more or less partial view of the species. By a comparison 

 between the species we shall be able to see in how far any of these 

 dimensions is of specific value. If we find that the ranges of variation 

 in two species overlap for any one character, that character cannot be 

 regarded as of primary rank in a specific description. In a dimension of 

 which the ranges of variation do not overlap in two species we have a 

 character of primary rank. The characters as set out in Table XTTT. will 

 now be examined in detail. 



