Fishes of the Western North Atlantic 341 



moderately convex toward tip, the distal margin only weakly concave, the inner corner 

 moderately rounded, the tip more narrowly so. 



Color. Described in life as white below, gray above, varying from very pale to much 

 darker, apparently as the result of environmental conditions, for those living over white 

 sand bottom may be very pale. Adults show no conspicuous fin markings. But in embryos 

 the tip and lower edge of the caudal and the margin of the second dorsal are sooty, and 

 perhaps the tips of the other fins likewise, in some cases, and these fin markings may per- 

 sist for a considerable time after birth, at least in some instances, for a 32-inch specimen, 

 apparently of this species, has been described as with second dorsal and anal dusky-tipped, 

 and the caudal wholly so." 



Size. Mature at a length of about seven feet, this species certainly grows to 10 feet 

 and perhaps somewhat longer, but reports of specimens longer than 12 feet may have 

 referred to C. longhnanus, with which it has often been confused. Specimens of 8 to 8^/4 

 feet have been reported as weighing 250 to 375 pounds; the weight of a male of 10 feet 

 caught off North Carolina is given as about 400 pounds." It has been suggested that the 

 three-foot Florida specimen illustrated in Fig. 60, taken in winter, was a yearling," 

 and it is probable that the young are born there in spring. Also, the advanced stage of 

 development of the embryos listed above indicates a length of perhaps 650 to 700 mm. as 

 usual at birth. 



Developmental Stages. Presumably development is viviparous, but the presence of 

 a yolk-sac placenta has not been definitely recorded for this species, so far as we are 

 aware. Embryos have relatively stouter bodies and blunter heads than their parents, but 

 they do not differ nearly so much from the adults in the shapes and relative sizes of the 

 fins as do those of longimanus ; like the adults, they are smooth-backed. Five or six 

 appear to be the usual number of young in a litter. 



Habits. This is a heavy, slow-swimming species, most common inshore in shoal 

 water, perhaps never very far from land except by accident. They are most often caught 

 around docks, at the entrances to the passages between islands, in estuaries and in harbors. 

 They often run up rivers for considerable distances, and it seems that they do not hesitate 

 to enter fresh water. Thus the series we have studied includes one from the Panama Canal 

 at Miraflores Locks, besides others from Lake Yzabal, Guatemala, a body of water that is 

 said to vary between fresh and brackish, and a 55-pound specimen has been reported, at 

 least by name, as having been caught in the Atchafalaya River, Louisiana, 1 60 miles from 

 the sea." We have also received a photograph of a shark four or five feet long that appears 

 to be of this species (unless possibly of the landlocked form nicaraguensis, which cannot be 

 determined from the photograph), taken 180 miles up the Patuca River, northeastern 

 Honduras." C. leucas is, in fact, the only Shark that is known to have permanently adapted 



21. Jordan and Gilbert, Proc. U.S. nat. Mus., 5, 1882: 243. 22. Bell and Nichols, Copeia, 92, 1921 : 17. 



23. Nichols, Bull. Amer. Mus. nat. Hist., 57, 1917: 874. 24. Gunter, Copeia, 1938: 69. 



25. This capture has already been reported, without attempt at specific identification (Strong, Explor. Smithson. 

 Instn. [1933], 1934: 46> 47i fig- 5s). 



