2 6o Memoir Sears Foundation for Marine Research 



Size. In American waters, R. radiata is hatched at a length of about loo mm from 

 snout to origin of first dorsal fin. But those of northern European seas, where the egg 

 cases average somewhat smaller (see p. 260), may hatch at a correspondingly smaller 

 size.i^^ It may mature through a wide range of sizes. Thus, a male only 21V4 inches 

 long (540 mm) was fully mature, whereas another about 33^/2 inches (845 mm), both 

 seen by us, has the claspers extending only slightly beyond the tips of the pelvics. On 

 another of about the same size as the latter (830 mm, or about 33 in.), the claspers 

 reach nearly halfway along the tail and appear to be fully developed; they are surely 

 so on another of 935 mm. Females as long as 1,020 mm (Nova Scotia) and as short 

 as 450 mm (North Sea and Norway) have been reported as containing eggs. The 

 Icelandic and American stocks tend to grow larger than those of northern Europe or 

 West Greenland. Thus, the maximum recorded length is only 450 mm for the North 

 Sea, about 600 mm for Norwegian waters,^" and 590 mm for West Greenland;"* but 

 the maximum size is 990 mm for Iceland, ^^^ 1,020 mm for the Scotian Banks,"* about 

 895 mm (35 V4 in-) for Georges Bank,"' 800 mm for Massachusetts Bay, and 935 mm 

 for the offing of New Jersey. 



Developmental Stages. The egg cases, flat on one side but strongly convex on the 

 other, are rough with narrow longitudinal ridges. A membrane-like mass of delicate 

 fibrils, matted together, extends along each lateral margin (over the surface as a whole 

 at deposition); each horn terminates in a slender fibril. i" The cases vary widely in size, 

 probably corresponding to the size of the parent fish. In the North Sea they average 

 about 48 by 34 mm (exclusive of horns), in Trondhjem Fjord 50-65 by 40—48 mm, 

 off West Greenland"' 45—68 by 26—51 mm, on the outer Nova Scotian Banks 77— 

 90 mm long from mothers 840—1,020 mm long, and in the estuary of the St. Lawrence 

 River (size of parents not recorded) 66—68 mm long.^-" The single egg case recorded 

 from Georges Bank, taken from a fish about 8 10 mm long (32 in.), measured 76 by 

 57 mm (3 by 27^ in.). 



At hatching the young already resemble their parents so closely (apart from 

 whatever vestiges of the embryonic caudal filament may persist) that their identification 

 presents no difficulty. This is one of the Skates for which monstrosities, such as those 



as is often true of the Gulf of Maine specimens. Some from Southwest Greenland and from the Newfoundland 

 Banks are more or less prickly above the eyes and have a few prickles scattered among the thorns, whereas others 

 are smooth above the eyes and between the thorns, as is commonly the case on New England specimens. However, 

 it may develop that there is some geographic variation in the average number of mid-dorsal thorns, for the maximum 

 number seen on any Gulf of Maine specimen has been i6, whereas there are i6 each on two out of six from West 

 Greenland and on two out of three from Norway. 



112. An embryo 84 mm long to origin of first dorsal (120 mm long to tip of tail, but with the latter still filamentous) 

 bears a yolk sac of considerable size, but the thorns have not yet been formed though their pattern is already evident. 

 The smallest free-living specimen we have seen, a newly hatched one from Georges Bank which had already lost 

 its caudal filament, was 100 mm long to first dorsal and 126 mm in total length. 



113. Smitt, Hist. Scand. Fish., 2nd ed., 1895: 1108. 114. In our Study Material. 



115. Saemundsson, Skr. Komm. Havunders. Kbh., 5, 1909: 125. 116. Vladykov, Nat. canad., 63, 1936: 225. 



117. Bigelow and Schroeder, Bull. U.S. Bur. Fish., 48, 1936: 325. 



118. For description of egg cases and of early stages in embryonic development, see Nordgaard (K. norske vidensk. 

 Selsk. Skr. [1915], Heft 2 [9], 1916: 24; and Vladykov, Nat. canad., 63, 1936: 223). 



119. Jensen, Spol. Zool. Mus. Hauniensis, 9, 1948: 30. 120. Vladykov, Nat. canad., 63, 1936: 225. 



