of the Fishery Board for Scotland. 



99 



The measuring board described in " On the Mackerel of the East and 

 West Coasts of Scotland," Eighteenth Annual Report of the Fishery Board 

 for Scotland, p. 295, 1900, was used for this part of the research. 



The accompanying diagram shows the points on the fish to which the 

 distances were measured. 



The point a represents the anterior end of the fish (mouth closed); 



a to 0. 



Distance from the tip of mandible to premaxilla, ... 

 Anterior edge of the orbit (for the length of the 



snout), ... 

 Base of first ray of ventral fin, 

 Opercular cleft, 



Base of first ray of pectoral fin, 

 Anus, 

 Base of first ray of first dorsal fin 



,, ,, last ,, ,, ,, ,, ,, 



„ „ first „ „ second „ „ 



,, ,, last ,, ,, ,, ,, „ 

 End of bend of lateral line, ... 

 Base of first ray of third dorsal fin, 



,, ,, last ,, ,, ,, ,, ,, 



„ ,, ,, ,, „ first anal ,, 



,, „ first „ „ second anal ,, 



,, ,, last ,, ,, ,, ,, ,, 

 Ventral base of tail fin, 



End of middle rays of tail ( = Length of Fish), 

 Tip of ventral ramus of tail, 



(b) The Girth at the Pectoral Region, at the Anus, and at Root of Tail. 

 — A thread was passed round the fish at the position and the two ends 

 crossed. A sharp knife was then drawn across the ends, cutting the 

 thread to the size of the girth. 



Lengths of the Pectoral, Ventral, and First Dorsal Fins. — In each case 

 the fin was measured from the base of the first ray to the farthest edge 

 of the fin. 



Diameter of the Eye. — For this the horizontal diameter of the orbit 

 was taken. 



The interorbital space was measured on the top of the head. 



The length of the ventral ramus of the tail was measured from the 

 base of the first fin-ray of the caudal fin on the ventral edge to the 

 extreme tip of the ramus. 



For the spread of the tail, i.e., the breadth, dorso-ventrally, the tail 

 was not distended to its fullest length ; it was simply flattened out. 



Length of Barbel. — For the measurement of the lengths of the barbel, 

 fins, and interorbital space, and diameter of the eye, a pair of conpasses 

 was employed. 



Enumeration- Characters. 



Number of rays in each of the dorsal and anal fins. 



Internal Characters. 



Number of vertebrae. The ural and hypural elements are together 

 counted as one vertebra. 



Number of the vertebra bearing the first haemal arch. 



Distance of the first haemal arch (crown of the arch) from the anterior 

 end of the fish. 



Shape of the skull and clavicle. 



