Fishes of the Western North Atlantic 515 



Species. It seems sufficiently established that the Greenland Sharks of the sub- 

 Arctic on the two sides of the North Atlantic (including the White Sea) and of neighbor- 

 ing parts of the Arctic seas belong to a single species, described first by Gunnerus in 1766 as 

 Sgualus carcharias, but which, under the rules of nomenclature, must be called micro- 

 cephalusy Bloch and Schneider, 1801, the name Sgualus carcharias having been used previ- 

 ously by Linnaeus, 1758, for a very different shark (p. 142). It is still an open question 

 what the relationship is between microcephalus and the very much smaller form that has 

 been reported repeatedly from the Mediterranean and from the coast of Portugal as 

 rostratus. The difficulty, as is so often the case, is that the older portrayals differ widely 

 as regards relative locations of the fins and shape of the head. It is even possible that more 

 than one species may be included among the supposed rostratus.' But if the more recent 

 illustrations of rostratus can be accepted as reliable, it diflFers from microcephalus in a rela- 

 tively much shorter interspace between the tip of second dorsal and caudal, relatively 

 larger fins, smaller denticles, strongly developed luminous organs, and in various skeletal 

 characters;' it also attains maturity when much smaller, and, still more important, it is 

 ovoviviparous.* 



The North Pacific representative of the genus has usually been considered identical 

 with the North Atlantic form. However, the first dorsal stands considerably farther rear- 

 ward in a Japanese specimen that we have examined' (as shown by Tanaka also") than is 

 ordinarily the case in Atlantic specimens, and its pectoral and caudal fins are larger; the 

 lower anterior and upper posterior margins of its caudal are much more strongly convex, 

 the distance from the tip of its second dorsal to the origin of its caudal shorter relatively, 

 its upper teeth are considerably broader, and the basal outlines of its lower teeth more 

 deeply incised. These differences seem sufficient to mark it off as a separate species. We 

 have therefore proposed the name pacificus for it.'' 



In all probability the Greenland Shark of Bering Sea and Alaska belongs to this 

 species. However, no detailed account of it has yet appeared, nor have we adequate mate- 

 rial for comparison. 



The Antarctic representative of the genus, known from a single specimen only, has 

 also been made the basis of a separate species, antarcticus Whitley, 1939. Its first dorsal 

 appears to stand even farther forward than in microcephalus, and critical examination may 

 reveal additional differences.* 



2. Brito Capello's measurements and illustration (J. Sci. math. phys. nat. Lisboa, 2, 1870: 141, pi. 9, fig. 2) repre- 

 sent both the snout and the caudal peduncle as much longer than in any other Somniosus. 



3. Burckhardt, Ann. Mag. nat. Hist., (7) 6, 1900; 559; Helbing, Nova Acta Leop. Carol., Si, 1904: 347 ff., pi. 8, 9. 



4. For a recent report of its embryo, see Borri (Atti Soc. tosc. Sci. nat., 44, 1934: loi). 



5. This is the specimen illustrated by Garman (Mem. Harv. Mus. comp. Zool., 36, 1913: pi. 15, fig. 1-3) as brevi- 

 finna. 



6. Fish. Japan, 5, 191 1 : pi. 13, fig. 32-36. 



7. Bigelow and Schroeder, Proc. New Engl. zool. CI., jj, 1944: 35. 



8. See Whitley (Fish. Aust., /, 1940: 152) for illustration of the unique specimen. 



