Medical Officers of the Army of India.

65

37º north to about 42º south; and H. asiatica, which occurs in various places
on the shores of the Indian Ocean, from Zanzibar to Java.

      The geographical distribution of such a strictly littoral genus is interesting
and suggestive, but for the moment our concern is with the habits and larval
forms of its species.

      The habits and larval stages of H . emerita have been fully described by
S. I. Smith in the Transactions of the Connecticut Academy of Sciences, Volume
III, 1874-78, page 311, and the first larval stage by Walter Faxon in the Bulle-
tin of the Museum of Comparative Zoology, Harvard, Volume V, 1878-79, page
253.

      According to Prof. Smith, Hippa emerita is gregarious, burrowing in the
loose sand near low-water-mark and using the hinder end of its body for this pur-
pose. Individuals placed in a suitable aquarium at once plunged beneath the
sand, but soon worked back towards the surface, and at length came to rest in
a perpendicular position, with the tips of the antennules and eyes just showing
above the surface. While in this position the currents of water from the gill-cham-
bers kept the overlying sand in constant motion. The peculiarly long antennæ
were never seen extended, but were always kept tucked in between the maxil-
lipeds.

      These remarks apply without modification to Hippa asiatica, which species
I had frequent opportunities of observing when the " Investigator" was survey-
ing the Orissa coast in 1889.

      According to Mr. Faxon, the larva of Hippa emerita leaves the egg as a
Zoaea with a smooth oval carapace which is produced anteriorly to form a broad
rather blunt rostrum but which has no dorsal or lateral spines. The abdomen
(judging from the figure) is bent beneath the carapace, and is described as ending
in a large broad plate-like telson, the convex posterior edge of which is fringed
with minute teeth. Two pairs of small antennæ are present, as well as mandibles
and two pairs of small and the only other appendages present, besides
the enormous eyes, are the two pairs of large biramous maxillipeds used in loco-
motion.

      The newly-hatched larva of Hippa asiatica, which I had opportunities of
examining-in January 1889, corresponds almost exactly with that of H. emerita
as described and figured by Faxon: the chief difference being in the rostral spine
which is longer in Hippa asiatica.

      (b ) As far as I can ascertain, the larva of Thenus orientalis though it is
known to be a Phyllosoma (see Richters in Zeitschrift für wissenschaftliche
Zoologie, XXIII, 1873, page 623) has not been described.