12 THE PLAGIOSTOMIA. 



ISUROIDEI. 



snout conical; spiracles present; caudal very long, axis rather low 



teeth triangular, compressed; no nictitating membrane; no caudal keels 



Vulpeculidae (page 30) 

 snout subcorneal; spiracles absent or minute; tail with keels and pits 

 caudal axis much raised, lower lobe produced; mouth inferior 



Isuridae (page 31) 

 snout broad; spiracles small; tail and body with lateral folds or keels 

 caudal axis much raised, lobe produced; teeth many, minute 



Rhincodontidae (page 41) 



Catuloidei. 



snout depressed; body short; tail without keels and pits; spiracles present 

 caudal long, axis little raised, lower lobe not produced 

 nasoral grooves and nasal cirri present; anal small 



Oredolobidae (page 43) 

 caudal short, axis not raised, lower lobe not produced; nasal cirri 

 absent or present 

 nasoral grooves absent or rudimentary . Calulidae (page 68) 

 snout broad, depressed; body long; first dorsal in advance of ventrals; 

 spiracles present 

 caudal short, axis little raised, lower lobe not produced; mouth very 

 large 

 nasoral grooves absent; teeth many, minute, 3-5 cusped 



Pseudotriakidae (page 103) 



Carcharinoidei. 



Two spineless dorsals, first above the body ; an anal; 5 gill openings; tail with 

 pits and a produced subcaudal lobe 

 snout depressed ; spiracle absent or present; no nasoral grooves; a nictitat- 

 ing membrane 

 teeth compressed, triangular, one series in function 

 head not expanded across the orbital region 



Carcharinidae (page 106) 

 head much expanded across the orbital region 



Cestracionidae (page 155) 



