THE OYSTER-CRAB 101 
was no longer especially necessary. That the crab may 
be at times useful to the mollusc seems after all not so 
very improbable, for at the approach of an enemy so 
nervous a creature as a crab would no doubt begin to 
scuttle about and in this way communicate its terror to its 
more apathetic companion, which would then naturally 
close its doors against the danger. Dr. H. Woodward has 
recently recorded a remarkable instance of a Pinnotheres 
found encysted in a pearl-like formation of the pearl- 
oyster, Meleagrina margaritifera. 
Pinnotheres veterum, Bosc, and Pinnotheres pisum 
(Linn.) are common European and British species. Guard 
and Bonnier suppose that under the latter name several 
distinct species have been confounded. Its Zoéa, long ago 
studied and drawn by Mr. Vaughan Thompson, is a 
singular-looking microscopic object. Among the names 
of other species some which indicate the animal’s resi- 
dence may be mentioned, as Pinnotheres ascidiicola, Hesse, 
from the coast of France, the Japanese Pinnotheres pho- 
lidis, de Haan, and Pinnotheres lithoddmi, Smith, from the 
Pearl Islands and Lower California. A similar indication 
is given in the generic name, Holothuriaphilus, Nauck. 
In ‘The Civil and Natural History of Jamaica,’ when 
speaking of a Pinnotheres, which he calls the Oyster-Crab, 
Patrick Browne says: ‘This little species is generally 
found with the Mangrove oysters, in their shells, where 
they always live in plenty, and spawn at the regular 
seasons ; and such as eat the oysters, do not think them a 
bit the worse for being accompanied with some of these 
crabs, which they swallow with the fish. They are very 
small and tender, and nearly of the same length and 
breadth, seldom exceeding a quarter of an inch either 
way.’ 
Hymenosima, Desmarest, 1825, was established under 
a name invented by Leach, and signifying a membrana- 
ceous body. ‘This is a character in which many members 
of the family partake. Hymenosoma orbiculare, Latreille 
and Desmarest, is a South African species. LHalicarcinus, 
White, 1846, is closely allied to Hymenosoma, but courts 
9 
