34 SORTATION. 



This leaves us with the double dorsal fishes having thoracic 

 ventrals. Two we can deal with on their lateral line, that row of 

 perforated scales running along the sides of so many species, the 

 holes in which communicate 

 with a muciferous duct lead- 

 ing to the head, a good ex- 

 ample of which was given 

 in the outline of the dentex 

 on a preceding page. In one 

 genus of this group, Caranx 



(the horse mackerel or scad), F j g I7 TEETH OF HAKE 



the lateral line is armed with 



bony plates, a further distinctive mark being the two spines in front of 

 the ventrals. In another genus, Sciczna (the shadow-fish), the lateral 

 line is continued through the tail to the outer edge of the caudal fin. 



The genera that remain can be sorted out according to the num- 

 ber of spines in the first dorsal. In Crystallogobius there are two 

 spines which are placed wide apart. In Aphia there are five spines. 

 In another of the gobies, the painted goby (Gobius pictus), there are 



6 spines in the first dorsal, the anal is without a spine, and the ven- 

 trals have a spine and 5 rays. The other gobies (Gobius) have 6 or 



7 spines in the first dorsal, and the anal has a spine. The two- 

 spotted goby (G. ruthensparri) is the only one with 7 spines ; the 

 one-spotted goby (G. minutus) is the only one with the dorsals wide 

 apart; the speckled goby (G. parnelli) has black fins with white 

 lines, the first dorsal ending in a black blotch ; the rock goby (G. 

 niger) has brown fins with whitish lines ; and of the two other 

 gobies, G. quadrimaculatus has four spots in a line on the hinder half 

 of the body, and G. pagandlus has the dorsals banded with orange. 



In Coitus the first dorsal has from 6 to 10 spines, the anal is 

 spineless, and the ventrals have a spine and less than 5 rays. There 

 are four species, one, C. quadricornus, having four short horns on 

 the top of its head, the others having no horns. The miller's thumb 

 (C. gobio) has a spine and 4 rays in its ventrals ; the long-spined 

 cottus (C. bubalis) has a spine and 3 rays ; and the father lasher (C. 

 scorpius) has no spine and only 2 rays. 



This leaves us with the two highest representatives of the perch 

 family, Labrax and Perca. In Labrax, of which there is only one 

 British representative, the bass (L. lupus), there are 8 or 9 spines 

 in the first dorsal, and the anal has 3 spines ; in Perca, the sole 

 representative being the perch (P. fluviatilis), the first dorsal has 

 14 or 15 spines, and the anal has only 2. Summarising as before, 

 we have : 



Ventrals thoracic 



Lateral line armed with bony plates 



Two spines in front of ventrals Caranx. 

 Lateral line continued through caudal fin Scicsna. 

 First dorsal of 2 spines, wide apart Crystallogobius. 

 First dorsal of 5 spines Aphia. 



