322 Memoir Sears Foundation for Marine Research 



corners not elongate; dermal denticles either overlapping or not, their blades with 3 or 

 more ridges, their apical margins toothed or not; axis of caudal raised only moderately; 

 upper labial furrow very short, at an obtuse angle with the jaw; no lower labial furrow. 

 Development viviparous, with well developed yolk-sac placenta in the few cases where it is 

 known (see pp. 359, 394). Characters otherwise those of the family. 



Range. Tropical and warm-temperate belts of all oceans, including the Mediter- 

 ranean, both inshore and on the high seas; also landlocked in Lake Nicaragua in fresh 

 water. 



Fossil Teeth, closely resembling those of Carcharhinus (perhaps including Hypofrion 

 and AprionoJon), have been described under various names from: Eocene, Africa ; Eocene 

 to Pliocene, Europe and North America; Oligocene to Miocene, South America; and Mio- 

 cene, West Indies. 



Species. Carcharhinus mdudes a much larger number of species than any other genus 

 of modern sharks and many of the most familiar of the larger sharks of warm seas. Its 

 members cover a wide range as regards teeth, the relative sizes and shapes of fins, and to a 

 lesser degree the relative positions of the latter. But the extremes are connected by such a 

 continuous series of intermediate stages in all these respects that attempts to subdivide the 

 genus have not been easy.^ In fact, the only alternative character which might form a sharp- 

 cut basis for such subdivision, from the standpoint of specific identification, is the presence 

 or absence of a mid-dorsal ridge. But the use of this would entail the generic separation of 

 species that closely resemble one another in other respects, and the union of others that do 

 not, which seems too high a price to pay for reducing the length of the generic Key, which 

 would be the only advantage gained. 



The genus has received much less attention than it deserves, no doubt due to the fact 

 that most of the species are rather large, with consequent paucity of specimens in collec- 

 tions. Many of the species resemble one another so closely in general appearance that little 

 or no dependence can be placed on published reports of occurrence unless accompanied by 

 some indication as to fins, teeth, etc. Therefore, we are very fortunate in having been able 

 to study specimens of all 1 3 species now known to occur in the western Atlantic ; finding 

 that while some of them look much alike on cursory examination, they are separable by 

 characters so precise and so little variable that specific identification is not difficult, although 

 attention to detail is required. 



The genus is as universally distributed in the warmer belt of the Pacific and Indian 

 Oceans as it is in the Atlantic, and some of its Indo-Pacific representatives are evidently 

 very close to some of the Atlantic species, if not identical with them. However, to attempt 

 to revise the genus as a whole would be idle without access to adequate material of at least 

 a majority of the supposed Indo-Pacific species, which we have not had. The following 

 Key is therefore limited to the western Atlantic. 



5. Whitley, in a series of papers, has recently broken the genus down into no less than nine genera and subgenera (see 

 Generic Synonyms, p. 321). But the characters on which these are based seem to us more appropriate for the 

 definition of species within the genus. 



