Fishes of the Western North Atlantic 275 



little posterior to axils of pelvics, crossed on posterior quarter by two irregular yellowish 

 white bands. 1^' 



Relationship to Extralimital Species. In the southern hemisphere R. spinicauda has 

 a close counterpart in R. griseocauda Norman 1937"* of the Patagonian-Falkland Islands 

 region. The resemblance between these two Skates is so close, in fact, that only a com- 

 parison of specimens from the two regions can show whether there are significant dif- 

 ferences between them. The relationship between the members of this pair thus parallels 

 that between R. radiata of the northern North Atlantic and R. doello-juradoil?ozx\ 1 933'^* 

 of Argentina, Patagonia, and the Falkland Islands (p. 255). Among Skates of the north- 

 eastern Siberian-Bering Sea region, R.violacea Uvarov 1935^^^ resembles R. spinicauda 

 most closely. But the former has only about half as many thorns along the tail as R. spini- 

 cauda^ and there is an extensive area free from prickles on either side of the mid-dorsal 

 belt of its disc. 



Size. Specimens measured (about nine males and females) have ranged from 740— 

 1,720 mm in length, showing this to be one of the larger Skates of northern seas. A 

 male 910 mm wide (hence about 1,340 mm long) with slender claspers was sexually 

 mature. 



Developmental Stages. Egg capsules, apparently of this species, in our Study Mate- 

 rial (p. 272), measure 137 by 90 mm and 142 by 95 mm. They are of the usual quadrate 

 shape, with nearly straight transverse outline at the end bearing the longer pair of horns, 

 concave at the end with the shorter pair. The lateral flanges are narrow, continue out 

 along the basal parts of the horns, and bear masses of fine filaments matted together and 

 more or less interconnected by a delicate membrane, as is true of various other Skate 

 eggs. In the preserved state these masses of filaments are irregularly scattered along the 

 flanges (chiefly near their extremities); but they may have been continuous along the 

 flanges when the eggs were first laid. On the larger specimen, one of the horns of the 

 shorter pair is about 115 mm long, with filamentous tip; all of the horns on both of the 

 specimens have lost their extremities. The most interesting feature of these capsules, 

 and one that sets them apart from those of any other Atlantic Skates whose eggs are 

 known, is that their entire surface, apart from the extremities of the horns and the 

 lateral flanges, bears a great number of low narrow longitudinal ridges, each close-set 

 with a single series of numerous stiff rod-like structures about two mm long, with com- 

 plexly dissected tips. On one of our capsules there are between 140—150 ridges on each 

 side, each with 200—220 or more rods, or a total upwards of 30,000 on each side, giving 

 the capsule a velvety appearance. 



Similar egg capsules, taken from shark's stomachs off Southwest Greenland, have 

 already been credited to R. spinicauda because they were certainly not referable to any 

 other Skate known from Greenland. i" And their identity as egg cases of R. spinicauda 

 is now made highly probable by the wedge-shaped anterior contour of the embryo con- 



153. On specimen seen. 154. Discovery Rep., 16, 1937: 26. 



155. Physis B.Aires, 11, 1935: 491; see also Norman, Discovery Rep., 16, 1937: 15. 



156. Bull. Acad. Sci. Leningrad [1935], 1935: 3, 431, 432, fig. i- 



157. Jensen, Mindeskr. Steenstr. Fods. Kbh., 2 [30], 1914: 33, figs. 10, 11; Spol. Zool. Mus. Hauniensis, 9, 1948: 56. 



