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PROCEEDINGS OF THE NATIONAL MUSEUM 



First dorsal fin fairly large, its height 1.1 to 1.2 times its base, and 

 1.2 in distance from posterior margin of eye to first gill opening; 

 length of rear tip of first dorsal 3.7 to 3.6 in first dorsal height; apex 

 of first dorsal moderately rounded, anterior margin weakly convex, 

 distal margin more strongly convex along its upper two-thirds but 

 concave below; origin of first dorsal varying from well behind to 

 almost above posterior (inner) corner of pectoral fin; rear tip of first 

 dorsal anterior to pelvic fin origin by a distance of about IK times 

 length of pelvic base. Second dorsal fin very small, short based but 

 with a rather long rear tip; height of second dorsal 1.2 to 1.0 times 

 its base, and one-tenth to one-ninth of height of first dorsal; length 



Figure 9.—Isurus oxyrtnchus, Scripps Inst. Oceanogr., 54-140, Baja Calif.: a, b, upper and 

 lower teeth, right side; c, d, first upper tooth, right side, anterior and lateral views, showing 

 incomplete cutting edge on lateral margin. (The jaw from which these teeth were drawn 

 is of comparable size to that of /. alaius in figure 8.) 



of rear tip almost twice second dorsal height; origin of second dorsal 

 well anterior to anal origin. Caudal fin somewhat lunate in outline, 

 ventral lobe shorter than dorsal lobe, terminal lobe strongly developed; 

 length of ventraJ Jobe 1.5 to 1.4 in dorsal lobe; length of terminal 

 lobe measiu-ed from tip of dorsal lobe to base of subterminal notch 

 4.2 to 4.4 in dorsal lobe. Anal fin similar in shape to second dorsal 

 fin but shghtly larger; origin of anal fin shghtly behind or just below 

 posterior end of second dorsal base. Pelvic fins moderately large, 

 anterior margins equal to or a Httle longer than bases, and only 

 slightly shorter than distal margins; length of pelvic base 1.7 to 1.9 

 in first dorsal base. Pectoral fins remarkably long, only slightly 



