Fishes of the Western North Atlantic 211 



inner edge of each of its nostrils bears a narrow barbel-like lobe directed outward and 

 rearward, a character that is not duplicated in any other Skate that we have examined. 2* 



Size. The length shortly after hatching (irrespective of whatever traces may persist 

 of the embryonic caudal filament) appears to average about 160-180 mm. ^^^ A male 

 598 mm long is still immature, its claspers extending only a little beyond the tips of 

 its pelvics; but one 850 mm long is in breeding condition, judging from the size of the 

 claspers, which reach about halfway along the tail. The largest female recorded was 

 860 mm long.^* 



Developmental Stages. The egg cases average about 1.5 times as long as broad, 

 exclusive of the horns; the egg cases measured have ranged from 81 — 125 mm in 

 length (apart from horns) by 56—80 mm in breadth." In general appearance they 

 resemble those of R. radiata and their margins are similarly flanged. However, their 

 blackish brown to golden yellow shells lack the rough transverse wrinkles with which 

 those of R. radiata are usually sculptured, but they are described as covered with silk- 

 like hairs when newly laid. 



Habits. R. hyperborea is at home in polar temperatures from hatching to maturity 

 and its eggs are incubated successfully and regularly in water as cold as 0° C (32° F) 

 or colder; so far it has not been taken in water warmer than 1.5° C.^* Furthermore, it 

 appears to be confined to depths greater than 100 fathoms (shoalest recorded capture 

 120 fath.) even in the subpolar part of its range; it occurs chiefly in depths greater than 

 150-200 fathoms, and it has been taken at a depth of 1,309 fathoms.-^ In the Nor- 

 wegian Basin, where the icy bottom water of polar origin is overlaid by a much warmer 

 layer, the upper boundary for R. hyperborea falls about at the transition between the 

 two water masses, i. e., at about 300 fathoms. But its failure to come into shoal water 

 in subpolar situations, such as the Greenland fjords, cannot be explained on the basis 

 of temperature. 



The nature of its teeth suggests that R. hyperborea feeds on active prey, which is 

 confirmed by the fact that the stomach of a specimen taken west of Spitzbergen con- 

 tained 50 large pelagic amphipods (Euthemisto libellula\ fragments of an Arctic prawn 



24. These barbels are pictured by Garman (Mem. Harv. Mus. comp. Zool., 24, i S99 : pi. 6, fig. 2) though not mentioned 

 by him. 



25. The smallest free-living specimen recorded measured 160 mm (Thielemann, VViss. Meeresuntersuch., Abt. Helgo- 

 land, N. F. 13, Heft 2, 1922: 195), but another of 180 mm still showed traces of the yolk sac (Koefoed, Rep. Sars 

 N.Atlantic Deep Sea Exped., 4 [i], Zool., 1927: 24). 



26. Vanhotfen, in Drygalski, Gronl. Exped. Gesellsch. Erdkunde Berlin, 2 (i), 1897: 127, as R. radiata; Jensen, Minde- 

 skr. Steenstr. Fods. Kbh., 2 (30), 1914: 23. 



27. For more detailed accounts of the egg cases, some positively identified because they were taken from the mother 

 and another by the embryo it contained, see Jensen (Mindeskr. Steenstr. Fods. Kbh., 2 [30], 1914: 25-26; Spol. 

 Zool. Mus. Hauniensis, 9, 1948: 41-43), and Thielemann (Wiss. Meeresuntersuch., Abt. Helgoland, N. F. /j, 

 Heft 2, 1922: 194, 197). 



28. Our specimens from Southwest Greenland (p. 206), and one reported earlier from Ilua Fjord, near Cape Farewell, 

 were from localities where the bottom temperature at the depth in question is probably below 1° C throughout 

 the year, to judge from the readings that have been taken at Julianehaab and in two adjacent fjords (Krummel, 

 Handb. Ozeanogr., i, 1907: 455; Jensen, Mindeskr. Steenstr. Fods. Kbh., 2 [30], 1914: 39). See Hansen (Rapp. 

 Cons. Explor. Mer, 123, 1949: 8—12) for secular variations in temperature off West Greenland. 



29. 142 fathoms (Barents Sea) to 1,309 fathoms (south of Jan Mayen) in the northeastern part of its range; 120 fathoms 

 down to 260 fathoms in Greenland waters. 



