NO- 3539 HAMMERHEAD SHARKS — GILBERT 61 



allometric change with an increase in length (head width, distance 

 from snout to symphysis, head length, distance between first and 

 second dorsal bases, and snout to pectoral insertion), the values given 

 for S. nana are about what one would expect in individuals of media 

 around 1,300 milhmeters long. Of the various measurements listed 

 for S. nana, only three (distance from snout to pelvic insertion, 

 horizontal diameter of orbit, and length of caudal fin) seem to fall 

 outside the range of variation one would normally expect to find in 

 a large individual of S. media. 



Thus, with few exceptions the proportional measurements in S. nana 

 and S. media are very similar, and those in which there is slight 

 disagreement are not sufficiently different to warrant recognition of 

 a second species. The contour of the anterior margin of the head, 

 another character that supposedly differentiates S. nana and S. media, 

 falls within the normal range of variation for S. media (as discussed 

 elsewhere in this paper). 



In conclusion, while the validity of S. nana cannot be categorically 

 denied until the natures of the chondrocranium and the pore patches 

 on the ventral siu-face of the head are known, I so far can find no 

 evidence to indicate that it is specifically distinct from S. media. 



Variation. — Sphyrna media shows more than the usual amount of 

 variation in configuration of the anterior margin of the head. Some 

 specimens have an evenly rounded head (fig. 156), while in others 

 the head is faintly lobate, with a slight median indentation or scallop 

 (fig. 146). Those individuals with more lobate heads may be dis- 

 tinguished only with difficulty from specimens of aS'. corona. That 

 this condition is not strictly a function of size is shown by the fact 

 that one of the largest specimens of S. media examined, a 900 mm. 

 male (UCLA 58-304) from Panama Bay, was at first identified as 

 S. corona on the basis of head shape. 



Variation in the median scallop on the anterior margin of the head 

 was found to result from a comparable variation in the tip of the 

 rostral cartilage. Considerable variation was found also in the degree 

 of development and/or presence of the accessory rostral cartilages, 

 a single series of specimens sometimes showing all degrees of develop- 

 ment. 



Range. — Sphyrna media occurs in the eastern Pacific, from the 

 Gulf of CaHfornia south at least as far as Panama Bay, in the southern 

 Caribbean, and in the southwestern Atlantic (map 5). 



The occurrence of Sphyrna media in the Caribbean is confirmed by 

 two specimens (USNM 79284, MCZ 500) from the Colon (Panama) 

 market, which were collected around the tm-n of the century. Pres- 

 ence of the species in this area is further substantiated by Stewart 



