THE ANOMURAN COLLECTIONS MADE BY THE FISH HAWK EXPEDITION 
TO PORTO RICO. 
By JAMES E. BENEDICT, 
Assistant Curator of Marine In vertebrates, U. S. National Museum. 
In classification the Anonmran crabs occupy a shadowy place between the 
Brachyura and the Macrura. In some systematic works in recent years the Anomura 
have been divided between these subdivisions under the names Brachyura a/nomaUa 
and Macrura anornalia. This does not, however, change the group from its inter- 
mediate position, nor, indeed, do more than indicate the value of its characters in 
the mind of an author. 
The Anomura are found in all seas, though the distribution is by no means even, 
by far the larger number being found in the tropical and subtropical belts. The family 
LitJwdidm is most numerously represented in the North Pacific Ocean. The hermit 
crabs are the best-known members of the Anomuran group; common in all latitudes, 
usually from the shore line to considerable depths, they present the variations of 
form that a world-wide distribution naturally gives. The soft and unprotected 
abdomen compels them to find something with which to cover it, and we find them 
in shells and sponges or overgrown with polvzoa or anemones. The great majority 
live in the dead shells of mollusks, changing from one shell to another as they grow 
or when for any reason they have occasion to seek another house. 
The necessity of changing shells as the crab grows is done away with in a curious 
manner in the case of some species. A hydroid envelops the shell and grows with 
the crab, or a sea anemone plants itself on the shell and covers it on all sides except 
the mouth, growing in the form which will furnish the best protection. In return 
for this kindly act the crab furnishes motive power for an otherwise stationary 
animal. One thing leads to another, and we often find the sea anemone and crab in 
close contact; the shell having, as it were, fitted the anemone to the crab, had lost its 
usefulness and been dissolved by one or the other of its captors. In the North 
Pacific the Albatross dredged many hermits living in sponges, the size of the sponge 
being disproportionately great to that of the crab. Here also the original home of 
the crab was in a shell, the shell in time being overgrown with a sponge. 
When the hermits move about they protrude their chelipeds or hands and the 
first two pairs of ambulatory feet; the posterior two pairs are very much reduced in 
size; their function as ambulatory feet is a thing of the past. In the Anomura 
the fifth pair are always more or less modified; in some the fourth pair are 
equally so, as in the hermits. The Dromias have the fourth and fifth pairs reduced 
in size and furnished with a small hook-like nail. By means of these modifications 
they are able to hold sponges or shells over their backs. In the Porcdlanidie the 
fifth pair are small and elevated so that they rest on the carapace. In the Lithodida \ 
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