22 THE PLAGIOSTOMIA. 



Nostrils small, at the edge of the snout, nearer to the tip than to the mouth. 

 Eyes large, about two thirds as long as the snout, lateral. Spiracle small, on a 

 vertical midway between eye and gill opening. Mouth large, nearly as long as 

 wide, subangular in front, nearly straight on the sides; labial fold rudimentary, 

 on the upper jaw, in the angle; a deep groove from the angle half way to the gill 

 opening. Gill openings seven, wide, close together, in front of the pectoral. 

 Teeth compressed in cusps and bases; upper without a median tooth, about 

 nine (9-10) laterals each with a slender, fang-like, curved, hooked cusp, without 

 or with one or two denticles or serrations on the inner edge of its base, and, 

 posteriorly at least, with one or two denticles on the outer; a few very small 

 teeth behind these laterals (above and below) ; lower median tooth with a 

 strong cusp at each side of which stands one or a pair of smaller ones ; at each side 

 of the median there are five large compressed, quadratic, pectiniform, lateral 

 teeth all of which are denticulate on the inner edge of the primary cusp and bear 

 four to seven (3-9) much shorter cusps on the outer side of the primary, the 

 number increasing backward. Upper jaw (pterygoquadrate) articulated closely 

 and rather firmly to the short postorbital process, against the side of the skull ; 

 hyomandibular weaker, more slender, and articulated to the side of the skull at a 

 lower level than in either Hexanchus or Notorynchus. Pectorals nearly as 

 broad as long, hind margins concave, angles rounded, bases closely bound with 

 the muscles of the side. Dorsal small, origin near a vertical from the ends of the 

 bases of the ventrals, hind angle produced, hind margin concave. Anal base 

 about as long as that of the dorsal, origin little forward of that of dorsal base, 

 fin narrow, outer edge very oblique, hind angle produced, length of base more 

 than half the distance from the caudal. Caudal long, less than one third of the 

 total length, tip broadened outward; subcaudal produced in an angle anteriorly, 

 narrow and separated from the tip by a notch posteriorly. Ventrals rather 

 narrow, outer margins very oblique. Scales minute, median keel strong ending 

 in a sharp point, a short less developed keel at each side of the median. 



In a young one of ten inches the snout is more depressed and has a deep 

 indentation in front of each nostril; the pectorals are more truncate, the hind 

 angles of the fins less produced, the lower angle of the subcaudal less prominent, 

 and the upper edge of the caudal is armed by three series of large modified scales. 

 The back of this specimen is brown to the middle of the flank, thence the lower 

 surfaces are whitish; the pectorals are dark brown to the wide margin of white 

 across the ends; ventrals and anal are white; dorsal white in forward half and 

 at base to the posterior angle, a large spot of black on upper half; a band of 



