THE PONTONIIDE 241 
fresh water, and, singular to relate, although they are in- 
habitants of distant localities, several of which are oceanic 
islands, yet all the species bear so close an affinity of form 
that itis difficult to determine one from the other by any 
permanent character. To explain this distribution, it is 
suggested that ova may be carried in mud on the feet of 
wading birds, and by this means species transferred from 
one locality to another even over great distances. The in- 
genious theory, already referred to, by which Mr. Thomas 
Belt accounts in general for the wide distribution of fresh- 
water species, does not seem applicable to those occupying 
oceanic islands. Genera related to Atya are Atyephijra, 
Brito Capello, 1857, for a Portuguese species, Paratya, 
Miers, 1882, conditionally proposed for the Japanese 
Ephyra? compressa of de Haan, T'roglocdiis, Dormitzer, 
18538, which inhabits caves in Carinthia, and Hvatya, 8. I. 
Smith, 1872, which belongs to Central America. 
Fumily 3.—Pontonide. 
The mandibles have a molar process and cutting edge 
but no ‘palp.’ The first pair of trunk-legs are subequal, 
slender, and chelate, the second unequal, one of the pair 
very large in the male. 
_ ‘Two genera are assigned to the family, both of which 
occur in the Mediterranean. 
Pontonia, Latreille (1818), 1829, has the dorsal surface 
flattened, and the rostrum dorsally flat. There is no 
ocellus on the hind margin of the eye. The first antennz 
have one of the two flagella bifid at the extremity, the 
second have a short but strong scale. The fully developed 
branchie are only four or five pairs. It is not correct to 
say that ‘ the telson carries no spine on the dorsal surface.’ 
Several species certainly have them. In Australian speci- 
mens received from Mr. I’. H. Haynes there are two pairs. 
The apical margin of the telson in the Australian species 
is fringed with six spines. The type species, Pontonia 
custos (Forskal), takes up its alole between the valves of 
a Pinna, and is supposed to be referred to by Aristotle 
when he says that a little shrimp (caridion) may take the 
