FISHES OF THE GULF OF MAINE 187 



The eggs of the latter are oval, 0.72 to 0.97 mm. in greatest diameter, with a 

 yellow oil globule of 0.25 to 0.31 mm., and are usually described as of an orange 

 tint. The larva are very slender, and about 7 mm. long by the time the yolk is 

 absorbed. The dorsal and anal fin rays are visible at about 1G mm., but the fins do 

 not assume their final outlines until the young fish are upwards of 25 mm. long. 

 The early larval stages are easily recognizable by their slender form combined with 

 the fact that the vent opens at one side and not at the margin of the larval fin fold, 

 so that it apparently ends blind just as among the cod tribe. The older larvas much 

 resemble the corresponding stages of the rock eel (p. 362) in their slim form and in 

 the location of the vent slightly behind the middle of the trunk (in the similarly 

 elongate larva of the herring tribe it is located farther back), but may be recognized 

 by the row of black pigment cells along the dorsal instead of the ventral side of 

 the intestine (p. 362), and by their pointed noses. The dorsal and anal fin rays are 

 visible when the larva is about 18 mm. long, but while the full number of the latter 

 are formed early, in the case of the dorsal fin the rays behind the vent are consider- 

 ably developed before those farther forward appear; and it is not until the little fish 

 is upwards of 25 mm. long that the tail begins to assume its forked outline, this 

 fact being a convenient field mark for distinguishing between the launce and the 

 herring, in which the tail is deeply forked from a much earlier stage. 



We have taken larval launce at only four stations in the Gulf, and then in 

 small numbers, an apparent rarity surprising with the adults so plentiful and with 

 young launce perhaps the most abundant of all fish fry in European seas. It remains 

 to be seen whether the Gulf of Maine actually is not a prolific breeding ground but 

 depends on immigration from elsewhere for the maintenance of its stock of launce, 

 or whether we have simply missed them by towing at the wrong time or place. 

 The rate of growth has not been studied. The young ones of 3 to 4 inches, which 

 are plentiful from July until September, are probably yearlings, while those of 

 5 inches and upward are probably 2 years old. 



Commercial importance. — It is only for bait that sand eels are of any com- 

 mercial value in the Gulf, for which purpose 67,S00 pounds were landed from the 

 traps in Massachusetts in 1919. 27 



THE MACKERELS. FAMILY SCOMBRID^E 



The mackerels are a very homogenous group, all of them agreeing in the 

 possession of a spiny as well as a soft dorsal fin, several small finlets behind the 

 latter and behind the anal, a very slender caudal peduncle, a deeply forked or 

 lunate caudal fin, a very shapely form tapering both to snout and to tail, and 

 velvety skin with small scales. All, too, are predaceous, swift swimmers, and 

 powerfully muscled, while all are fish of the open sea and more or less migratory. 



In the following key we mention all species so far actually recorded from 

 within the limits of the Gulf of Maine, but it would not be surprising if still other? 

 were to stray in from the open Atlantic on occasion. 



" A second species of launce (the Arctic Ammodytes dubius Reinhardt) has been reported from Boston by Giinther (1882), 

 and from Woods Hole by Smith (1S98), but it is probable that the specimens in question were merely large Ammodytes americanus. 

 In fact it is doubtful whether there is any sound distinction between the A. dubius of Greenland and the European A. tobianus 

 on the one hand, or the American A. americanus on the other. 



