MUSEUM OF COMPARATIVE ZOOLOGY. 93 



where joined to the laterals, is an approach toward the Trigonidse rather than 

 toward the Eaise. 



The lack of canals on the lower surface and the junction of pleurals and 

 orbitals sufficiently distinguish the Torpedoes from other families. 



Narcine. 



Narcine brasiliensis (Plate XXXIII.). Apparently there are no traces of 

 the canals on the ventral surface. On the back there is a very simple arrange- 

 ment of the system. The lateral passes directly to the end of the vertebral 

 column. Only a moderate degree of prominence is given the scapular curve. 

 Rather widely separated at the shoulders, the laterals converge toward the 

 back of the head. The tubules are short and not many. At the outer edges 

 of the batteries the pleurals encroach but little on the pectorals. Half-way 

 from the eye to the margin they unite directly with the suborbitals. 



The occipitals are long. About midway from the eye to the end of the 

 snout the cranials dwindle and disappear, after sending off a group of short 

 tubules in front of the eye. The curve around the. eye described by the orbi- 

 tal is somewhat regular, and the canal ends near the margin. It sends out a 

 couple of short branches near the spiracle, and some shorter ones in front of 

 the junction with the pleural. A strong tubule reaches backward from an 

 angle in the pleural, opposite the scapular bends. From the lack of branch- 

 lets, the small size of the tubules, etc., the total length of the system is much 

 below the average of the order. 



Potamotrygon. 



Potamotrygon motoro (Plate XXXIV.). Upon the shoulders of this species 

 the laterals bend outward in a variety of curves. The anterior of these, the 

 greater ones, are concave, the posterior convex. A very little behind the girdle 

 the pleurals are met. There are two pre-scapular tubules, which do not en- 

 close an area. Behind the pleural there are several post-scapulars more or less 

 disposed to unite soon after leaving the main tube. The pleural starts from 

 several branches which form scapular enclosures. Backward from the aural the 

 laterals describe the outlines of a goblet, with the bowl extended forward, and 

 closed by the aural. The occipital tubules are not far behind the ends of the 

 latter. At the fontanelle the cranial curves are but moderate. Tubules are 

 numerous on the head, and backward; in general they branch two or more 

 times. From the laterals the pleurals pass backward and outward, rather more 

 than in the sketch, until well out on the fin, where they form a somewhat 

 sharp angle and turn forward in a broad curve: in front of the eye they turn 

 inward, and, passing under the orbital, they descend at the fore part of the 

 skull. Long tubules, with small groups of branchlets at their ends, extend 

 laterally toward the margins. Two or more tubules join the pleural and the 

 orbital. A branch goes back from the orbital at the eye, and, in front of the 



