248 THE PLAGIOSTOMIA. 



pectorals large, broad; first dorsal entirely forward of the origins of the ventrals, 

 and second dorsal one length of its base behind their tips. Subcaudal narrow, 

 narrowing toward each end, separated from the tip bj' a shallow notch; supra- 

 caudal wider, broadening backward; tip of moderate width. 



Brown, lighter beneath, rostrum longitudinall}^ striped with brown and light. 



IMelbourne, Hobson's Baj^; Tasmania. 



Pliotrema. 



Pliotrema Regan, 1906, Ann. Natal mus., 1, p. 1, pi. 1. 



This genus has six gill clefts on each side. Aside from these there appears 

 very little to separate it from Pristiophorus. Whether this number of clefts 

 has been continuously retained from a six-gilled ancestry or has been secured by 

 specialization, or by reversion, from five-gilled ancestors is not yet determined. 

 It is certain, however, that its possession in connection with the general structure 

 and affinities gives us no reason for placing the family any nearer to the Hexan- 

 choids. 



Pliotrema w^4.rreni. 



Pliotrema loarreni Reg.\>;, 1906, Ann. Natal mus. 1, p. 1. pi. 1. 



Body elongate, width and depth about equal, flattened beneath and bearing 

 a well-developed dermal ridge at the lower edge of each side on the tail. Scales 

 small, with a median keel and with or without a lateral keel at each side of it, 

 absent from distal portions of the fins. Snout length four and two fifths times 

 its greatest width. Rostral teeth compressed pointed unequal, lai'ger denticu- 

 late on the hinder margin. Nostril reached by the barbel, further from its root 

 than from the angle of the mouth. Forty to forty-four rows of teeth on the 

 upper jaws, thirty-one to tliirt5"-four on the lower. Dorsals subequal, origin of 

 first above hind extremit}^ of the pectoral. Caudal feebly heterocercal, upper 

 lobe well developed. About 750 mm. in total length. 



The coast of Natal and from False Bay, Cape of Good Hope, in about forty 

 fathoms. 



Rhixidae. 



The Rhinidae ai-e small sharks of the sands and the rocks of the sea bottom 

 with habits hke those of some Batoids, which have modified themselves in struc- 

 tures and shapes in similar directions. They possess some features evidently 



