428 bulletin: museum of comparative zoology. 



Velellidae Brandt. 



Velella velella (Linne). 



Medusa velella Linne, 1758, p. 660. 



(For synonymy, see Bigelow, 1911b, p. .353). 



The common Velella was taken at Stations 10,163, 10,200, 10,207 

 a total of al)out twenty specimens, ranging in length from 5-50 mm. 



Geographical Distribution. 



Considerable interest naturally attaches to the first collection of 

 animals of any group from an oceanic area, even though there be 

 nothing in depth, temperature, salinity, or locality, to presuppose 

 important faunal differences from neighboring regions. The collec- 

 tions obtained by the Bache are a case in point, for while many 

 pelagic coelenterates are known from the American and West Indian 

 coastal waters, and from the inner margin of the Gulf Stream on the 

 one hand; from Bermuda and the tropical Atlantic on the other, there 

 are practically no previous records of Medusae or Siphonophorae 

 from the oceanic triangle between Cape Hatteras, Bermuda, and the 

 Bahamas. This, as a glance at a chart will show, is a characteristically 

 oceanic region, and as such, general knowledge of the distribution of 

 pelagic animals makes it safe to predict that the characters of its 

 medusan and siphonophore fauna will depend directly on its physical 

 characteristics. Although this part of the oceanic basin is north of 

 the tropics in latitude (27°-35° N.), its mean annual temperature is 

 upwards of 22° c. on the surface waters, (Schott, 1902, taf . 9), cooling to 

 about 19°-20° in mid-winter; 18° or higher at 200 meters (1917; 

 Schott, 1902, 1912). And its salinity, 36%o or more at all depths 

 down to 500 meters (1917a; Schott, 1902, 1912), is correspondingly 

 high. But this warm salt ocean water contrasts very sharply with 

 the low temperatures and salinities of the coast water on the conti- 

 nental shelf, on the one hand, and on the other with the North At- 

 lantic abyssal water (3.5°-4°; about 34.9%o), at and below 1,800 

 meters (1915, 1917). 



The Florida, and the Antilles currents both skirt the region in 

 question, the former bringing the water of the Gulf of Mexico, with its 

 denizens, through the Straits of Florida; the latter following the 

 Bahama Bank; beyond which they merge, as the Gulf Stream, to 



