126 Memoir Sears Foundation for Marine Research 



Interspace between: ist and 2nd dorsals 24.8, 25.5; 2nd dorsal and caudal 8.7, 



8.7} anal and caudal 8.0, 7.2. 



Distance from origin to origin of: pectoral and pelvics 27.9, 28.3 ; pelvics and anal 



16.9,17.2. 



Figure 19. Isurus oxyrinchus. A Upper and lower teeth of specimen pictured in Fig. l8, about natural size. 

 B Side view of anterior part of jaws of a large Cape Cod, Massachusetts, specimen (Harv. Mus. Comp. Zool., 

 No. 816), about J/2 X. 



Trunk fusiform, considerably more slender than in Lamna nasus, its height at origin 

 of 1st dorsal (where highest) about equal to distance from eye to 2nd gill opening, or about 

 15% of total length, tapering both rearward and forward. Caudal peduncle very much 

 flattened dorso-ventrally, but broadly expanded laterally and sharp-edged as in other 

 Isuridae (Fig. 1 8 B), but without the secondary keel below it that is characteristic of nasus. 

 Sides smooth. Lateral line not prominent. Upper and lower caudal pits strongly developed 

 as deep furrows, nearly transverse to peduncle, or perhaps slightly arcuate (convexity 

 rearward) in some specimens. Denticles small, closely imbricate, with 3 to 5 ridges, and 3 

 marginal teeth, the median the longest but often worn down. 



