106 THE PLAGIOSTOMIA. 



Carcharinidae. 



Body elongate; head and snout depressed; tail compressed; eyes lateral, 

 provided with a more or less perfectly developed nictitating membrane; nostrils 

 below the snout; mouth crescent-shaped, inferior; two dorsals, not preceded 

 by a spine, the first dorsal forward of the ventrals; an anal fin. 



In this family the teeth have been the principal aid in classification, both 

 among the living and among the fossil forms that have been discovered at 

 numerous levels since the early Tertiary. 



Teeth compressed, onecusped; one series in function; a nictitating membrane; 

 caudal pits 

 spiracle minute 



teeth not serrated, subequal in both jaws, oblique, notched 



Loxodon (page 107) 

 spiracle absent 



teeth not serrated, bases swollen, points slender, oblique 



Physodon (page 108) 

 teeth not serrated, bases not swollen, cusps oblique in both jaws 



Scoliodon (page 109) 

 teeth not serrated, cusps rather slender, upper nearly erect, lower erect 



Aprionodon (page 117) 

 teeth with serrations on the base in the upper series only 



Hypoprion (page 120) 

 teeth serrated, some or all, on bases and cusps 



first dorsal near the pectorals . . Carcharinus (page 123) 

 teeth serrated, slightly swollen, cusps oblique 



first dorsal near the ventrals . . . Galeus (page 145) 

 spiracles minute 



teeth serrated on both jaws, upper teeth oblique 



Thalassorhinus (page 146) 

 teeth large, subequal on both jaws, oblique 



labial fold along upper jaw; subcaudal long Galeocerdo (page 148) 

 teeth on the upper jaw only denticulated 



labial folds on both jaws, subcaudal long Hemigaleus (page 149) 

 spiracles small; caudal pits rudimentary; subcaudal short 



teeth serrated, notched, oblique; labial folds Eugaleus (page 152) 



