Fishes of the Western North Atlantic 77 



except that Chlamydoselachus and the Pristiophoridae are each made a distinct suborder 

 for the reasons stated below (pp. 94, 532). 



Key to the Suborders of Modern Sharks 

 I a. Anal fin present. 



2a. 6 or 7 gill openings. 



3a. Margins of ist gill openings not continuous across throat 5 upper and lower 

 teeth notably unlike toward center of mouth. Notidanoidea, p. 77. 



3b. Margins of ist gill openings continuous across throat} upper and lower teeth 

 similar in center of mouth as well as along its sides. 



Chlamydoselachoidea, p. 92. 

 2b. Only 5 gill openings. 



4a. Dorsal fins preceded by stout spines j teeth toward center of mouth in each 

 jaw markedly different from those toward its corners. 



Heterodontoidea,°" p. 94. 

 4b. Dorsal fins not preceded by spines; teeth toward center of mouth of same 

 basic type as those toward its corners. Galeoidea, p. 95. 



lb. No anal fin. 



5a. Snout of only moderate length, without lateral teeth or barbels. 



6a. Trunk subcylindrical ; eyes lateral; anterior margins of pectorals not over- 

 lapping gill openings. Squaloidea, p. 449. 

 6b. Trunk much flattened dorsoventrally; eyes dorsal; anterior margins of pec- 

 torals far overlapping gill openings. Squatinoidea, p. 533. 

 5b. Snout greatly elongate, as a narrow beak, armed on either side with sharp teeth, 

 and with a long fleshy barbel. Pristiophoroidea," p. 5 3 2 . 



Suborder NOTIDANOIDEA 



Characters. Anal fin present; only one dorsal fin, without spine; either 6 or 7 gill 

 openings, all anterior to pectorals; margins of ist gill openings not continuous across 

 throat; snout not beak-like, without lateral teeth or barbels; upper and lower teeth toward 

 center of mouth widely dissimilar, but essentially similar to those toward corners. Trunk 

 subcylindrical (shark-like); eyes lateral; anterior margins of pectorals not expanded for- 

 ward beyond ist gill opening; nostrils separate from mouth, anterior margins without 

 barbels; eye without nictitating fold or membrane; spiracles present; segmentation of ver- 

 tebral column incomplete, but centra more or less differentiated, with axial canal somewhat 

 contracted in its passage through them; notochord partially constricted segmentally in 



35a. For a recent account of this group, see Smith, B. G. (Dean Memor. Vol., Amer. Mus. nat. Hist., 8, 1942). 



36. These "Saw Sharks" superficially resemble the true "Sawfishes" (Pristidae) which, however, fall among skates 



and rays (Batoidei), they having ventral gill openings as well as the edges of the pectorals attached to the sides 



of the head anterior to the gill openings. 



