41 6 Memoir Sears Foundation for Marine Research 



8 1 with 86 B). It shares a median indentation in the anterior outline of the head with both 

 tudes and bigelowi, but it is separable from them at a glance by the facts that the corners 

 of its mouth are considerably anterior to the outer rear corners of the head (hammer) and 

 that the free rear tip of its second dorsal is considerably longer than the anterior margin of 

 the fin J it is further separated from tudes by its smooth-edged teeth. The hammer shape of 

 its head obviates any danger of confusing it with tiburo. 



Description. Proportional dimensions in per cent of total length. Female, 554 mm., 

 from Galveston, Texas (Harv. Mus. Comp. Zool., No. 35826). Female, 639 mm., from 

 Rio de Janeiro (Harv. Mus. Comp. Zool., No. 462). 



Trunk at origin of -pectoral: breadth 9.4, 8.55 height 1 1.9, 1 1.6. 



Snout length in front of: outer nostrils 4.4, 4. i ; mouth 7.4, 7. i . 



Eye: horizontal diameter 2.3, 2.4. 



Mouth: breadth 6.8, 7.0 ; height 3.8, 3.8. 



Nostrils: distance between inner ends 20.8, 20.2. 



Gill opening lengths: ist 3.6, 3.7; 2nd 3.6, 3.7J 3rd 3.5, 3.7; 4th 3.2, 3.5; 5th 



2.5,2.8. 



First dorsal fin: vertical height 13.4, 12.7 j length of base 12.4, i i.o. 



Second dorsal fin: vertical height 2.9, 3.35 length of base 4.1, 3.1. 



Anal fin: vertical height 3.4, 3.3 ; length of base G.t^, 5.3. 



Ca«^a/^«; upper margin 33.4, 3 1.0 J lower anterior margin 11. 7, 12.0. 



Pectoral fin: outer margin 13.2, 13.OJ inner margin 4.9, 5.OJ distal margin, lO.O, 



11.3. 



Distance from snout to : ist dorsal 26.4, 28.2; 2nd dorsal 56.O, 6o.2} upper caudal 



66.6., 69.O} pectoral 22.4, 22.9; pelvics 41.3, 46.6; anal 55.O, 57.2. 



Interspace between: ist and 2nd dorsals 20.6, 23.3; 2nd dorsal and caudal 7.4, 



6.7} anal and caudal 6.3, S-(>- 



Distance from origin to origin of: pectoral and pelvics 20.6, 22.7; pelvics and anal 



12.8, II. 7. 



Trunk strongly compressed, its height at ist dorsal about Y^ its length to origin of 

 caudal, with moderately arched dorsal profile. Back without mid-dorsal ridge. Body sec- 

 tor to cloaca, a little longer than tail sector. Caudal peduncle about % as wide as deep, the 

 upper precaudal pit strongly marked, subrectangular in outline, the lower pit only weakly 

 indicated as a short, semilunar furrow. Dermal denticles much as in zygaena, partly over- 

 lapping and with skin partly exposed, the blades thin, moderately arched, small specimens 

 usually with 3, but large with 4 or 5, sharp-topped ridges running back about half the 

 length of the blade, the marginal teeth much as in zygaena, the axial a little the longest; 

 pedicels very short, moderately slender. 



Head about V3 of length to origin of caudal, sloping evenly forward to anterior mar- 

 gin, very broadly expanded in hammer form but with posterior edges (outward from 

 the neck) sloping only a little rearward; the breadth at eyes about 1.2 to 1.3 times as great 



