The True Sharks 199 
in warm seas and known as tiger-sharks (Galeocerdo maculatus 
in the Atlantic, Galeocerdo tigrinus in the Pacific). 
The species of Carcharias (Carcharhinus of Blainville) lack 
the spiracles. These species are very numerous, voracious, 
armed with sharp teeth, broad or narrow, and finely serrated 
on both edges. Some of these sharks reach a length of thirty feet. 
They are very destructive to other fishes, and often to fishery 
apparatus as well. They are sometimes sought as food, more 
often for the oil in their livers, but, as a rule, they arc rarely 
caught except as a measure for getting rid of them. Of the 
many species the best known is the broad-headed Carcharias 
lamia, or cub-shark, of the Atlantic. This the writer has taken 
with a great hook and chain from the wharves at Key West. 
These great sharks swim about harbors in the tropics, acting as 
Fig. 141.—Cub-shark, Carcharias lamia Rafinesque. Florida. 
scavengers and occasionally seizing arm or leg of those who 
venture within their reach. One species (Carcharias nicara- 
guensis) is found in Lake Nicaragua, the only fresh-water shark 
known, although some run up the brackish mouth of the Ganges 
and into Lake Pontchartrain. Carcharias japonicus abounds in 
Japan. 
_ A closely related genus is Prionace, its species Prionace 
glauca, the great blue shark, being slender and swift, with the 
dorsal farther back than in Carcharias. Of the remaining 
genera the most important is Scoliodon, small sharks with 
oblique teeth which have no serrature. One of these, Scoliodon 
terre-nove, is the common sharp-nosed shark of our Carolina 
coast. Fossil teeth representing nearly all of these genera 
are common in Tertiary rocks. 
Probably allied to the Carchartide is the genus Corax, 
containing large extinct sharks of the Cretaceous with broad- 
