128 ON MYLIOBATIS AND PTEROCEPHALA. 



Length of body from snout to root of tail, 20 inches. 



Length of tail, 24 inches. 



Total width across pectoral fins, 327 inches. 



Width of head between the eyes, 4I inches. 



It may be well to compare with this specimen one or two of allied 

 species previously in the Museum collection. 



Of these the first appears to be Myliohatis Jussieui or Zygobates 

 of Agassiz. 



In this species the head is more flattened than in M. Aquila, and 

 the margin of the snout is straight, giving a quadrangular shape to 

 the head. 



The Pectoral Fins are narrower and more falciform than in 

 M. aquila. 



Length of body, 14 inches. 



Length of Tail, 285- inches. 



Extreme width across pectorals, 26I inches. 



Tail, whip-like, without spine. 



Dorsal fin at the root of tail. 



Teeth like those of M. aquila, except that there are 3 rows of 

 transversely extended denticles with the smaller ones at the sides. 



It will be observed that in this species the shape of the head 

 approaches that found in the genus next to be described. 



The tail is considerably larger in proportion to the body, and the 

 width across the pectorals relatively greater than in M. aquila. 



The remaining specimen is one of Pterocephala (Couch), and 

 there is also the head of another individual of the same genus in 

 the collection. 



In this family the head is flattened, concave in front, and has on 

 each side a projection 2| or 3 inches long, which has caused one 

 species to be called the Ox Ray. This projecting horn is formed 

 of a rolled or. twisted fin, terminating in a point. The spiracles are 

 smaller than in Myliobatis. 



Tail, long and whip-like, without spine. 



Pectoral Fins rather narrow, straight and pointed. 



