56 



Memoirs of the Indian Museum. 



[Vol. II, 



Granted that there are three species of Aiitohatis,' it is necessary to inquire how 

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

 the diagnosis is very difficult, 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 s})ecimens of the Indian forms : — 



Aetobatis guttata (vShaw). 



Size considerable (adult male 125 cm. across the disk). 



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



Tatl mnch longer than disk, always bearing at least one serrated .spine, often two, 



sometimes three. 

 Colour. — Dorsal surface of yomig 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, hke Mv/iohatis nicn/iofii, 

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



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

 ings of Indian specimens of Aetobatis and for comparing them with the original figures of -1. flagelhtm, 

 which I have not been able to consult. 



' Gilbert and Starks (Mem. Calif. Acad. Set., iv, p. iS, 1904) give the width of the disk of a speci- 

 men from Panama Bay as (115 mm. but do not state its sex. 



