Note on the Family of Myliobatoids. 135 



tail feathers extending over both webs ; the tail feathers are 

 narrower than those of eximia, and the dark band at the end 

 of the tail is about half as wide as in that species. 



XIII. — Note on the Family of Myliobatoids, and on a New 

 Species of .^Etobatts. 



By Theodore Gilt,. 

 Bead April 3, 1S65. 



The family named Myliobatides by Miiller and Henle, is 

 an eminently natural and distinct group, but contains several 

 genera, exhibiting characters of very unequal value, and which 

 ma} 7 be grouped into two tribes well distinguished by peculiari- 

 ties of dentition. For their first separation, we are indebted 

 to Prof. Agassiz. 



The MyliobatincB Ag. include only such species as have 

 several longitudinal rows of angular interlocking teeth, with 

 plane surfaces ; Myliobatis, Ilolorhinus, Rhinoptera, and 

 Zygobatis belong to it.* 



Aetooatince Ag. have a single longitudinal row of transverse 

 plane teeth, and the dental plane of the lower jaw is flat, more 

 or less convex or angular at the middle, and projects far for- 

 wards. Aetobatis and Goniobatis have been named as genera. 



Holorhinus is perhaps scarcely generically distinct from 

 Myliobatis, although its ventral fins are much wider and rhom- 

 boid, while Zygobatis does not appear to be sufficiently distinct 

 from Rhinoptera. Myliobatis and Rhinoptera are conse- 

 quently alone adopted, and to them may perhaps be added two 

 which have been hitherto confounded with .Rhinoptera, but 

 which seem entitled to distinction ; they may be distinguished 

 as follows : 



* I am unable to understand what the "genus Trikeras' of Harless (1850) is 

 intended to embrace. 



