The Spotted Eagle Ray. 



287 



It is characterized by a single row of large 

 teeth on each jaw. I have figured it in table D, 

 figures I and 2 [here reproduced as text-figs. 9A 

 and 9b]. The teeth of the lower jaw, figure 2 

 [text-fig. 9A of this paper] are transverse, while 

 those of the upper jaw are more or less arched, 

 figure I [here text-fig. 9B]. 



A. Upper jaw (Tab. D, fig. 2). B. Lower jaw (Tab. D, fig. i). 



Text-fig. 9. — Jaws of Myliobatis {Aetohatis) narinari, after Agassiz. 



It seems unbelievable that Agassiz should have allowed to slip into his 

 work so great an error as the above transposition of the jaws, but he did so 

 and he repeats it in the explanation of the plates. Where he says upper, 

 we should read lower, and vice versa. He next goes into a microscopical 

 examination of the tooth structure, into which we will not follow him here.^ 

 This occurs on pp. 79 and 80 of the general introduction to his "Poissons 

 Fossiles," volume iii. However, on pages 325-326 he gives the following 

 illuminating description of the jaws and their functions. 



This genus (Aetobatis) is characterized by the form of the jaws, of which the lower 

 projects in front, while the upper is much shorter and is squarely cut off. Both are fur- 

 nished with a single row of transverse teeth without lateral chevrons. The lower jaw is, 

 as in the genus Myliobatis, longer than the upper jaw (tab. D, fig. i) [present text-fig. 9B]. 

 The bone of this jaw is longer than wide. The dental plate, whose surface is almost flat 

 in its whole extent, does not cover all the surface of the jaw. In return, its anterior part 

 projects considerably over the jaw, and as the teeth are arched in front, this only makes the 

 anterior edge more salient. Since all the teeth are parallel with each other, their surface 

 offers the aspect of strips curved and joined, the one to the other. The last tooth alone is 

 transversely cut off. The anterior part of the dental plate, which is lightly shaded in figure 

 2 of table D [present text-fig. 9A], is used for the rubbing of the two jaws against one another. 

 The upper jaw is much wider than long. The dental plate covers it unlike that of the 

 lower jaw, in that the strips are almost straight and only a little bent at their edges, and 

 thus they surround the anterior border of the jaw in such a manner as to form an arched 

 surface in front of the gullet. This part of the dental plate is used for rubbing against the 

 point of the lower jaw. 



By comparing these drawings with the figures of the Beaufort specimens, 

 either the photographs (figs. 22 and 23, plate ix) or the outline drawing 

 (text-fig. 14), it will be seen that in the jaws of my fish the lower teeth are 

 much more sharply angled, especially in front; while in the upper jaw the 

 teeth of Agassiz's ray are much more concave than mine. The grinding 

 surfaces are in both sets of jaws practically the same, covering five teeth 

 in the upper and nine in the lower jaw. 



1 Agassiz notes that the specimen from which these jaws were excised came from the coast of Brazil. 



