66 BULLETIN OF THE BUBEAU OF FISHEKIES 



its two diverging troughs, in both of which there is a dominant though perhaps not 

 a constant indraft along the bottom, the result being that while its route parallels 

 those of the two preceding species in the eastern part of the gulf, it crosses below 

 them at a lower level in the western, an interesting phenomenon illustrated in the 

 accompanying chart (fig. 33) . No doubt this applies in general to the three bathy- 

 metric groups which these three chretognaths typify. 



The possibility that visitors may occasionally penetrate the gulf from the mid- 

 depths of the Atlantic basin below, say, 300 meters, deserves a word. 



The successive deep-sea expeditions, from the Challenger in 1872 to 1876 down 

 to the Michael Sars in' 1910, have found an abundant and varied pelagic fauna in 

 the Atlantic below the level to which strong sunlight penetrates. Generally speak- 

 ing, the adults of this community live well below 200 meters (many of them chiefly 

 below 400 to 500 meters) and many of them are characterized by a peculiar coloration. 

 Thus, those dwelling so deep that red light reaches them feebly, if at all, often exhibit 

 a very dense pigmentation (Hjort, 1911 and 1912; Bigelow, 1911a), many fishes of 

 this category being black with phosphorescent organs, decapods dark red, and 

 medusas either of a beautiful, translucent, deep claret color or opaque chocolate, 

 tints quite unknown among jellyfishes in shallow water. This extreme development 

 of pigment is so characteristic of this whole faunal group that the latter is often 

 referred to as the "black fish-red prawn" community. 



At a higher level (that is, in the zone between 150 and 500 meters, but neverthe- 

 less below the reach of the wide diurnal fluctuations in illumination to which the 

 surface waters are subject) there exists an entirely distinct series of fishes of quite 

 different aspect, which as a rule are "laterally compressed, with a mirrorlike silvery 

 skin; when colored, the back is generally blackish brown, and the resplendent mirror- 

 like sides of the body blue or violet. The eyes are large, very often telescopic, 

 and the body i s provided with a number of light organs" (Hjort, 1912, p. 628). 

 They are accompanied by sundry medusas, which parallel them in their pale pigmen- 

 tation but brilliant iridescence, as I have pointed out elsewhere (Bigelow, 1911a, p. 6). 



It is a fortunate chance for the oceanographer that many of the bathypelagic 

 animals are so distinctively colored, because their presence in any numbers any- 

 where in shoal water over the continental shelf would be the best of evidence of 

 an upwelling of Atlantic water from the mid-depths or deeper, a type of oceanic 

 circulation that has evoked considerable discussion as a possible factor in maintain- 

 ing the low temperature of the coastal waters off the eastern United States. Conse- 

 quently, the presence or absence of the black fish-red prawn community within the 

 Gulf of Maine is a question of some moment, and it is in the hope of encouraging 

 others to keep a sharp lookout for it there that I have devoted the preceding lines 

 to the general appearance of its members. No doubt this planktonic community 

 is represented at the appropriate level all along the continental slope off the United 

 States, for it occurs generally over the whole Atlantic basin from high latitudes to 

 low. We encountered it over the 1,500-meter contour off Cape Sable on March 19, 

 1920 (station 20077), the following being a partial list of its more noticeable repre- 

 sentatives in hauls from 500 and 800 meters: Several black lantern-fishes (genus 

 Myctophum) ; a specimen of the curious deep-sea snipe eel (Serrivomer beanii) , 45 



