234 THE PLAGIOSTOMIA. 



small. Gill openings moderate to narrow. Two small dorsals, spine absent or 

 rarely rudimentary. No anal fin. Tail short, without lateral folds or caudal 

 pits. Scales uniform. 



Head subcorneal 



first dorsal small, behind the pectorals, spine absent or small 



second dorsal much longer than the first . Euprotomicrus (page 234) 

 first dorsal small, behind the pectorals, spine absent 



second dorsal nearly equal the first, near the pectorals 



Scymnorhinus (page 236) 

 second dorsal nearly equal the first, near the ventrals 



Isistius (page 237) 

 Head depressed; eyes small 



first dorsal small, behind the pectorals 



second dorsal smaller . . . Heteroscymnus (page 239) 



second dorsal about equal the first . . Somniosus (page 240) 



Euprotomicrus. 



Euprotomicrus Gill, 1864, Proc. Acad. nat. sci. Phil., p. 264. 

 Squaliolus Smith & Radcliffe, 1912, Proc. U. S. nat. mus., 41, p. 683. 



Body elongate, fusiform. Snout short, subcorneal; nostrils near the end. 

 Mouth transverse, with a deep straight groove at each angle. Upper teeth 

 small, subulate; lower larger, compressed, smooth-edged, with sharp somewhat 

 oblique cutting edges. Eyes without nictitating folds. Spiracles rather wide, 

 behind the eye. Gill openings narrow, in front of the pectorals. First dorsal 

 small, without or with a small spine, behind the pectorals. Second dorsal much 

 longer, without a spine. No anal fin. Caudal short and deep. Scales minute, 

 flattened, uniform. 



First dorsal distant from the pectorals, little behind mid length 

 spine absent or rudimentary 



a median tooth in the lower jaw . . . bispinatus (page 235) 

 teeth of a lower series 17. Base of first dorsal 5 of that of second, 

 interspace six times the former. Hind edge of orbit above mouth. 

 Vertical diameter of spiracles 5 that of orbit. 



head gg of total length hyalinus (page 235) 



First dorsal near pectorals, in front of mid length 

 spine small, not much exposed 



pectorals reaching little behind origin of dorsal laticaudus (page 235) 



