SYNOPSES OF NORTH-AMERICAN 
INVERTEBRATES. 
X. THE OxyrHYNCHOUS AND OXYSTOMATOUS CRABS OF 
NORTH AMERICA. 
MARY J. RATHBUN. 
Tue Oxyrhyncha include the large family of Maiidz, or 
* spider crabs," so called on account of their slenderlegs. The 
body is usually narrow in front, sometimes suborbicular, but 
always with a beak or rostrum, as in the common “ spiders” 
(Libinia) of the Atlantic coast. The Maiidz are all provided 
with numbers of hairs, either hook-shaped or straight, varying 
in form and arrangement in the different genera and species. 
In order to conceal themselves from enemies these crabs cover 
their backs with algze and sedentary animals, as sponges, tuni- 
cates, and bryozoans, which are held fast by the hairs and live 
and grow until their host is unrecognizable. This is notably 
so in Oregomia gracilis. Some species, as those of Collodes, 
are covered with slimy adherent mud. 
The Parthenopidz, the second and smaller division of the 
Oxyrhyncha, are easily distinguished by their broad, triangular 
carapace, very long, usually trigonal chelipeds, and short, deli- 
cate walking legs. They often resemble fragments of stone 
with sharp angles, or with eroded or nodular surfaces. 
The Oxystomata comprise several families widely different 
in their general appearance. Of the Calappide the best known 
are the species of Calappa, ** box crabs,” or **shamefaced crabs," 
from the chelipeds which are large and of unusual shape, with 
cockscomb-like crests on the upper margin of the hands, and 
Which in flexion are pressed tightly against the inferior surface 
of the carapace like a shield. This arrangement is said to pro- 
tect from attack any morsels of food they may be devouring. 
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