FISHES OF THE GULF OF MAINE 473 



0. Mouth large, gaping back as far as the eye; jaws and teeth nearly equally developed 



on both sides 7 



Mouth small, not gaping back as far as the eye; the jaws nearly straight on the upper 

 side and curved on the lower side 8 



7. Tail slightly forked; lateral line arched just behind the gill opening Halibut, p. 473 



Tail slightly forked; lateral line nearly straight Greenland halibut, p. 481 



Tail rounded; lateral line nearly straight American plaice, p. 482 



8. Lower side of head with large open mucus pits; 100 or more rays in the long (dorsal) 



fin Witch, p. 511 



Lower side of head lacks open mucus pits; less than 90 dorsal fin rays 9 



9. Lateral line arched behind the gill opening Dab, p. 495 



Lateral line nearly straight 10 



10. Top of the head between the eyes rough with scales 



Winter flounder (including also the Georges Bank flounder), p. 501 



Top of the head between the eyes naked and smooth Smooth flounder, p. 50S 



,. 



Fig. 238.— Halibut (.Hippoglossus hippoglossus) 



165. Halibut (Hippoglossus hippoglossus Linnaeus) 



Jordan and Evermann, 1896-1900, p. 2611. 



Description. — This is not only the largest but one of the best characterized of 

 flatfish, its most obvious diagnostic characters, apart from its size, being the facts 

 that it lies on the left side; 44 its mouth is large, gapes back to the eyes, and is 

 armed with sharp curved teeth; its tail is emarginate, not rounded; its two ventral 

 fins are alike; and its lateral line is arched abreast of the pectoral fin. Further- 

 more it is a narrower fish, relatively, than most of our flounders (only about one- 

 third as broad as long) but very thick, and its eyes are more widely separated than in 

 most flounders. The dorsal (long) fin (98 to 105 rays) commences abreast of the 

 eye and runs back the whole length of the fish, broadening but slightly for the first 

 third of its length and then abruptly, to narrow again toward the caudal peduncle. 

 The anal is similar in outline but shorter (73 to 79 rays), originates close behind 

 the pectoral, and is preceded by a sharp spinelike projection of the post-abdominal 

 bone, which projects in young fish but is hidden by the skin in old fish. The two 

 pectoral fins are unlike, the one on the upper (eyed) side of the fish being obliquely 

 pointed while the fin on the lower side is rounded. The rather small ventrals, 

 which are situated before the pectorals and are separated from the anal by a 



" Left-handed halibut have occasionally been caught. 



