56 



Memoirs of the Indian Museum. 



[Vol.. II, 



Granted that there are three species of Aëtobatis,^ it is necessary to inquire how 

 they can be distinguished from one another. If only dried specimens are examined, 

 the diagnosis is very difhcuh, if not impossible, and as regards the Atlantic form I am 

 wholly dependent on published figures and descriptions. The following table gives 

 the differences that are apparent from careful examination on the one hand of these 

 figures and descriptions and on the other of fresh specimens of the Indian forms : — 



Character. 



.4. guttata. 



A. narinari. 



.4. flagellum. 



Snout 



Conical, bluntly pointed, 



Rounded at the tip, much 



Pointed, straight, much 





distinctly retroverted, at 



broader at the base than 



longer than broad at the 





least as broad at the 



long, straight (?). 



base. 





base as long. 







Coloration of dorsal 



Uniform dark slate-grey 



The whole disk including 



Disk in the adult of a 



surface. 



in the young, ornamen- 



the head covered with 



uniform dark greenish 





ted with bluish spots, 



whitish spots both in the 



bronze colour, without 





which are confined to 



young and the adult. 



spots. 





the posterior half of the 









disk in the adult. 







Size 



Diameter of disk in adult 



Diameter of disk ^ in adult 



Diameter of disk in adult 





c? at least 125 cm. 



? 51 cm. 



c? 47 cm. 



Habitat 



Tropical parts of the In- 



Both sides of the Atlantic ; 



Red Sea. Bay of Bengal. 





dian Ocean. 



Gulf of Guinea, Amer- 

 ican coast as far north 

 as Virginia, West Indies. 





Aëtohatis guttata (Shaw). 



5î,2:e considerable (adult male 125 cm. across the disk). 



Disk shaped much as in Myliohatis nieuhofii, but quite naked. 



Tail much longer than disk, always bearing at least one serrated spine, often two, 



sometimes three. 

 Colour. — Dorsal surface of young of a uniform dark slate-grey, without a trace of 



spots. The spots on the disk of the adult are confined to the posterior half. 



They are of a bluish tint and are edged with a faint greenish halo. Their size 



varies considerably. The ground colour of the back of the adult has, in fresh 



specimens, a beautiful greenish refulgence. 



This is a very common species in the Bay of Bengal and, like Myliohatis nieuhofii, 

 is evidently gregarious and probably also migratory in habits, at least while it is young. 



' I am much indebted to Mes.srs. Boulenger and Tate Regan for examining a photograph and draw- 

 ings of Indian specimens of Aëtohatis and for comparing them with the original figures of 4. flagellum, 

 which I have not been able to consult. 



^ Gilbert and Starks {Mem. Calif. Acad. Sei., iv, p. 18, 1904) give the width of the disk of a speci- 

 men from Panama Bay as 615 mm. but do not state its sex. 



