428 THE PLAGIOSTOMIA. 



nium prominent. Tail long, slender, whip-like, bearing on the basal portion a 

 small dorsal fin and behind it in most genera a serrated spine. 



Rostral fins united in one lobe 



teeth in more than three rows on each jaw 

 side of head not free from the pectorals 



caudal spine present . . . Myliobatis (page 428) 



side of head free from the pectorals 



caudal spine absent .... Aetomylaeus (page 434) 

 caudal spine present .... Pteromylaeus (page 437) 

 teeth in one row on each jaw 



caudal spine present .... Aetohatus (page 440) 



Myliobatis. 



Myliobatis Cuv., 1817, Reg. anim., 2, p. 137. 



Disk broad. Head moderately prominent. Pectorals slightly falciform, 

 continued along the side of the head to the end of the snout, where they are joined 

 forming a single lobe. Teeth tessellate, in 7 rows, median broader, lateral 

 narrow. Anterior nasal valves confluent in a broad flap with free margin in 

 front of the mouth. Ventral fins short, broad. Dorsal small, between the 

 ventrals. A serrated spine above the base of the tail behind the dorsal. Tail 

 long, slender. 



Numerous species have been determined among Tertiary fossils, and others 

 from those of the Cretaceous and the Jurassic. 



Temperate and tropical seas. 



Snout short, broad, rounded 



flange connecting pectorals and rostrals rather wide 

 pectorals with broad, rounded tips 



dorsal origin 1 length of the base behind the bases of the ventrals 



californicus (page 429) 

 pectorals with tips of moderate width 



dorsal origin 2 lengths of the base behind ventral bases 



peruvianus (page 430) 

 pectoral tips somewhat pointed, blunt 



dorsal origin 3 lengths of base behind ventral bases 



goodei (page 430) 



