Memoirs of the Indian Museum. 
[VOL. II 
5Ö 
Granted that there are three species of Actohatisf 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 specimens of the Indian forms : — 
Character. 
. 4 . guttata. 
A. narinari. 
. 4 . flagellum. 
Snout 
Conical, bluntfi’ 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 
base as long. 
long, straight (?). • 
base. 
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 
the posterior half of the 
disk in the adult. 
young and the adult. 
spots. 
Size 
Diameter of disk in adult 
Diameter of disk '^ in adult 
Diameter of disk in adult 
c? at least 123 cm. 
9 51 cm. 
c? 47 cm. 
Habitat 
Tropical parts of the In- 
dian Ocean. 
Both sides of the Atlantic ; 
Gulf of Guinea, Amer- 
ican coast as far north 
as Virginia, West Indies. 
Red ,Sea, Bay of Bengal. 
Aetohatis guttata (Shaw). 
Size considerable (adult male 125 cm. across the disk). 
Disk .shaped much as in Myliohatis nieuhofU, 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 Messrs. Boulenger and Tate Regan for examining a photograph and draw- 
ings of Indian specimens of Aëtobatis and for comparing them with the original figures of A. flagellum, 
which I have not been able to consult. 
Gilbert and Starks (Mem. Calif. Acad. Set., 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. 
