PECULIARITIES OF PLA.ICE FROM DIFFERENT FISHING GROUNDS. 3l7 



The exposure and enumeration of the vertebrre are operations that 

 take some time, and by omitting them I was able to examine a larger 

 number of specimens. I omitted also the mean height of the caudal 

 peduncle, the determination of which did not appear to be susceptible 

 of great accuracy, and I did not follow Duncker in combining together 

 head-length and height of body. 1 added the examination of another 

 character, namely, the number of the tubercles, whose prominence or 

 flatness I also noted. 



The characters I have examined are therefore the following ; — 



1. Maximum height of body without fins. 



2. The length of the head, from the apex of the lower jaw to the 

 end of the opercular bone, on the upper side. 



3. The length of the caudal peduncle, from a line joining the ends 

 of the marginal fins to the middle of the line of articulation of the 

 caudal fin-rays. 



4. The length of the caudal fin, from the latter point to the end of 

 the middle rays. 



5. The number of the tubercles on the head behind the eyes. 



6. The number of the gill-rakers on the first branchial arch, upper 

 side. 



7. The number of the dorsal rays. 



8. The number of the ventral rays. 



9. The number of ciliated rays in the dorsal and ventral fins. 



10. The ciliated (spinulated) scales on the head and body. 



11. The maturity or immaturity of each specimen. 



The measurements of lengths were made with a millimetre scale and 

 a pair of dividers, and they were only taken to the nearest millimetre. 

 It did not appear that greater accuracy was possible. The body of a 

 plaice is not rigid like that of a crustacean, but any part of it may be 

 stretched or compressed a fraction of a millimetre, so that any greater 

 accuracy of measurement would have been apparent and not real. No 

 such qualification applies to the enumerations of numerical characters, 

 which are absolute, and were made with the greatest care. The lengths 

 of parts after measurement were calculated as hundredths of the total 

 body-length, which was measured from the apex of the lower jaw to the 

 end of the tail. To obtain this length the fish was laid upon the 

 measuring-rod, and the lower jaw was pushed into contact with the 

 vertical surface of a piece of wood placed upright at one of the lines 

 of the measure, the length at the end of the tail being then read off 

 directly. The measure was always taken with the lower jaw just closed 

 and not pressed. As the lengths were only taken to millimetres it 

 seemed useless to calculate the proportions to higher fractions than 

 hundredths of the body-length. The fish varied from about 200 to 



