FISHES OF THE GULF OF MAINE 15 



Key G — Continued 



15. No ventral fins, fishes capable of inflating themselves with air 



I Puffer and porcupine-fish families key, p. 297 



Ventral fins present; can not inflate themselves with air 16 



16. Dorsal fin runs whole length of back, from nape to base of caudal, which it joins; 



barbel on chin; form eel-like Cusk (cod family in part), p. 462 



Dorsal fin occupies only one-third or less of back behind nape, leaving open space 

 as long as fin between it and base of caudal; no barbel on chin; form not eel- 

 like Mummichog family key, p. 155 



Key H 



Fishes as in Key G, except that at least the forward one-third of the dorsal fin is spiny (from No. 22, p. 12). There is no adipose 

 fin behind the rayed dorsal, nor fleshy flap in front of it. 



1. Rear part of dorsal fin soft rayed 2 



Whole length of dorsal fin spiny 7 



2. Sides of head bony, with knobs or spines 3 



No knobs or spines on sides of head 4 



3. Sides of head with conical spines; spiny portion of dorsal fin at least as long as soft 



part; body laterally compressed Rockfish family, p. 304 



Sides of head with low rounded knobs; spiny portion of dorsal fin considerably shorter 

 than soft part; body tadpole-shaped-- Deep-sea sculpin (sculpin family in part), p. 329 



4. Ventral fins much longer than pectorals; eye very large Big-eye, p. 261 



Ventral fins no larger than pectorals; eye not very large 5 



5. Pectorals pointed; body much compressed Sea bream family key, p. 263 



Pectorals rounded; body not much compressed 6 



6. Rear (soft) portion of dorsal fin nearly as long as anterior (spiny) part; anal much 



higher than long Sea bass (sea bass family in part), p. 251 



Rear (soft) portion of dorsal fin less than half as long as spiny part; anal much longer 

 than high Gunner family key, p. 280 



7. Mouth strongly oblique; no ventral fins Wrymouth, p. 368 



Mouth not strongly oblique; ventral fins present (very small in one species) 



Blenny family key, p. 359 



THE LAMPREYS. CLASS MARSIPOBRANCHII 



Except for Amphioxus and its allies, the lampreys are the most primitive of 

 vertebrates, their skeletons being cartilaginous and their skulls hardlj' differentiated 

 from the vertebral column. They have no true jaws, no ribs, no shoulder or pelvic 

 girdles, and no paired fins. They are eel-like in appearance, but are easily dis- 

 tinguishable from the true eels and, indeed, from most of the true fishes by the 

 pecuhar jawless sucking mouth situated at the tip of the snout, and from all Gulf 

 of Maine eels by the absence of pectoral fins. 



THE HAGFISHES AND LAMPREYS. FAMILIES MYXINID.S; AND PETROMYZONID.a; 



These two groups are easily distinguished by the fact that the hags have but 

 one gill opening on each side, one continuous fin on the back, and several barbels 

 on the snout, whereas in the true lamprej's there are seven gill openings on each 

 side, the fin on the back is separated into dorsal and caudal portions, and there are 

 no barbels on the snout. 



