438 THE PLAGIOSTOMIA. 



the side of the head, the ventrals are more elongate and narrow and the spiracles 

 open more upward and less to the side. The teeth are tessellate, in seven rows : — 

 a median row of very broad teeth at each side of which are three very narrow 

 ones. The tail is long and slender; it bears a serrated spine behind the dorsal. 



Origin of dorsal fin far behind bases of ventrals 



back brown with transverse markings and spots of white 



asperrimus (page 438) 

 Origin of dorsal above ends of ventral bases 



back uniform brown hovina (page 439) 



Origin of dorsal near ends of pectoral bases 



back greenish grey with irregularly distributed spots of white 



punctatus (page 439) 



Pteromylaeus asperrimus. 



Myliobatis asperrimus Jord. & Everm., 1898, Bull. 47, U. S. nat. mus., p. 2754; Gilbert & Starks, 

 1904, Mem. Cal. acad. sci., 4, p. 19, pi. 3, f. 6. 



Disk nearly twice as broad as long, anterior margins convex, posterior 

 concave, outer angles slightly blunted. Head prominent, crown transversely 

 convex, narrowing toward the snout and the mouth. Snout produced, pointed; 

 rostral fins not continuous with the pectorals, at a lower level, narrower than 

 the cranium, forming a single flexible lobe. Skull prominent in the preorbital 

 region, excavated in front of the fontanel. Anterior nasal valves confluent in 

 a broad flap reaching the mouth, free at the lateral edges and behind, with a 

 shallow notch in the middle. Spiracles large, twice the length of the eye, 

 partly visible from above. Teeth in seven rows, median four to five times as 

 broad as long, more or less fused, outer narrow. Ventrals moderate, longer 

 than broad, rounded posteriorly, considerably extended behind the pectorals. 

 Dorsal small, as long as the spiracle, rounded above and behind, origin about 

 twice the basal length farther back than the bases of the ventrals. Tail slender, 

 very long, more than three times the length of the body. On young individuals 

 the caudal spine has a rudimentary appearance; it is situated at a distance behind 

 the dorsal equal to about two lengths of that fin. Skin rough with small spines. 



Measurements of an immature specimen from Panama are as follows: — 

 length of disk 19, length of tail 59^, and width of disk 31 inches. 



Back brown, ashy or greyish, crossed by stripes of white, fainter anteriorly, 

 and farther back giving place to numerous spots of irregular sizes and shapes, 

 as large as the eye to very small. In cases the edges of snout, disk, and dorsal, 

 and the tail are black. 



