Fishes of the JVestej'n Noyth Atlantic 519 



Teeth f^ in specimen counted (up to j^ reported), widely unlike in the 2 jaws; 

 upper teeth thorn-like, tapering gradually to tip,'* moderately stout, very slightly 

 recurved and flattened anteriorly (thus subtriangular in cross-section); lower teeth sub- 

 quadrate, about Yi as broad as high, except that the outermost 3 or 4 are relatively much 

 broader and lower, each overlapping the next outermost, their cusps smooth-edged, deeply 

 notched outwardlv and so strongly oblique that inner margins are nearly parallel with the 

 jaw, forming a continuous saw-like cutting edge (much as in Centroscymnus) , the basal 

 sectors with a strong longitudinal ridge; about 3 series functional as a rule in upper jaw, 

 I or 2 series functional in lower, depending on the stage in their replacement." 



Pectorals, dorsals and pelvics all very small. First dorsal brush-shaped, about V4 as 

 long at base as head, and about 3 to 4 times as long as high, its anterior edge very sloping, 

 apex rounded, posterior margin nearly straight or weakly concave, its free lower posterior 

 corner nearly or quite as long as base, its origin on mounted specimens about midway 

 between tip of snout and origin of caudaP" or posterior to axil of pectoral by a distance 

 I to 2 times as long as its own base. Interspace between ist and 2nd dorsals about as long 

 as from snout to ist or 2nd gill opening. Second dorsal nearly as long as ist at base, but only 

 about % as high vertically, with more broadly rounded apex, its origin over rear end of 

 bases of pelvics. Distance from tip of 2nd dorsal to origin of caudal about as long as base 

 of 2nd dorsal, or a little longer. Caudal Y^ to % of total length, its posterior margin 

 notched subterminally, about opposite end of caudal axis; its lower lobe about % as long 

 as upper lobe along upper margin of fin, the re-entrant contour included between the 

 two lobes considerably more obtuse than a right angle. Pelvics about as long at base as 2nd 

 dorsal or a little longer and about as high vertically, with broadly rounded apices and 

 tapering tips. Pectoral between Yz and Y2 as long as head, with nearly straight outer mar- 

 gin, moderately rounded tip, and much more broadly rounded inner corner. 



Color. Described as varying in life between coffee brown or black and ashy-gray, 

 purplish-gray, or slaty-gray, below as well as above, changing to bluish-gray if the epider- 

 mis is rubbed off, as often happens after capture; the sides are sometimes tinged with 

 violet; the back and sides are crossed by numerous indistinct dark bands, at least in some 

 specimens, or with numerous indistinct whitish spots. Vestigial luminous dots, not func- 

 tional, are reported'' as scattered on the top and sides of the head, in a band along the 

 lateral line, and on the caudal. 



Size. This is one of the larger sharks, and by far the largest of typically Arctic fishes. 

 It has been said to reach a length of 24 feet, but few, if any, actually grow to so great a 

 size, for the longest of which we find definite record'* was 21 feet, with specimens of 16 to 

 1 8 feet unusual, although occasionally taken. The largest western Atlantic specimens whose 



14. They closely resemble those of Centroscytnnus in general appearance but are recognizable as Somnlosus by their 

 progressive taper; in Centroscymnus they are definitely lanceolate (cf. Fig. loo A-C with 94. B, C, H). 



15. For discussion of this process in squalids with lower teeth of this type, see p. 65. 



16. Garman (Mem. Harv. Mus. comp. Zool., j(5, 1913: pi. 15, fig. 4) so pictures it also for a Massachusetts speci- 

 men newly caught. 



17. Burckhardt, Ann. Mag. nat. Hist., (4) 6, 1900: 562. 18. Jenkins, Fish. Brit. Isles, 1923= I^S- 



