NO. 3537 SHARK GENUS ISURUS — GARRICK 683 



tapered, anterior (outer) corners moderately rounded; length of 

 anterior margin of pectoral slightly greater than head length measured 

 from tip of snout to most anterior part of fifth gill opening; when 

 adpressed to side of body with anterior pectoral margin horizontal, 

 anterior (outer) pectoral corner reaches about 90 percent of distance 

 from pectoral origin to pelvic origin. 



Color. — Grayish black above, white below; underside of snout 

 and around mouth at least partly dusky, more so in largest specimen; 

 dorsal fins and both lobes of caudal fin dusky black; pectoral fin 

 dusky black above except for a translucent to white area at posterior 

 (inner) corner; underside of pectoral fin white but with a narrow 

 dusky band along anterior margin, and a broader dusky-black edging 

 to anterior (outer) corner and outer half of distal margin ; pectoral fin 

 in largest specimen, in addition, with some black mottlings under- 

 neath ; pelvic fin dusky black on anterior half of upper surface, white 

 posteriorly and below except in largest specimen in which underside 

 is partly black mottled; anal fin in holotype white, with a dusky-black 

 blotch anteriorly; anal fins in paratypes with more dusky-black 

 coloration, only distal margins remaining more or less white. 



Vertebrae.— Vertebral counts as in table 2. Centra very regular 

 over entire length of vertebral column. Centrum diameter con- 

 siderably greater than centrmn length, even in longest monospondy- 

 lous centra at posterior region of abdomen. Diplospondyly occurs 

 above anterior third to middle of pelvic base. 



~^^^ — of penultimate monospondylous centrum=0.63 to 0.67 

 Diameter 



Length of penultimate monospondylous centrum _ ^ ^^ ^^ ^ ^^ 

 Length of first diplospondylous centrum 



Discussion. — The specific name of /. alatus is the Latin adjective 

 alatm=wmged, and is given in reference to the extremely long 

 pectoral fins of this species. 



In view of the wide distribution of the few known specimens of 

 /. alatus (central Pacific to Indian Ocean), it is rather surprising that 

 the species has not been recognized before. The chief reason for this 

 may be that it is a truly oceanic species, not coming mshore as does 

 /. oxyrinchus. If this is the case, it is understandable that it has not 

 been taken during routine oceanographic explorations, few of which 

 have been equipped to catch fishes as large as isurid sharks. The 

 comparatively recent discovery of the abundance of other oceanic 

 sharks such as Carcharhinus Jalciformis and C. longimanus in the 

 western North Atlantic is a parallel situation. The larger eyes of 

 /. alatus suggest the possibility that it lives in rather deeper water than 

 /. oxyrinchus. 



