260 
CRUSTACEANS. 
sometimes double and of great length. On its dorsal surface the carapace is 
usually roughened with spines or tubercles, and frequently furnished with hooked 
hairs. These crabs frequent deep water, and, at least, on the English coast, are 
regarded by fishermen as spiders. The characteristics of this group are shown 
in the figures of two British species, the thornback crab (Maia squinado ) and the 
long-beaked spider-crab (Macropodia longirostris). Also belonging to this tribe is 
Macrochira kcempferi, which is not only the largest crab, but the largest 
crustacean known. It inhabits the seas of Japan, and is said to be able to span 
eleven feet with its outstretched pincers. 
A peculiarity of many of this group is their extreme untidiness, owing to the 
quantities of seaweeds, zoophytes, and other marine objects affixed to the carapace 
and limbs; and it has been ascertained that the presence of these extraneous 
bodies is not the result of chance, but that they are placed there, presumably 
for the purpose of concealment, by the crabs themselves. This feat they are 
enabled to perform owing to the flexibility of their pincers, and to the hooked 
hairs and spines with which the carapace is studded. Some examples of Hyas, 
deprived of their covering of foreign bodies, were placed under observation in an 
aquarium of which the bottom was covered with a layer of sponge. Contrary 
to their habitual sluggishness of manner, the crabs appeared much perturbed, 
running first to one side then to the other in the aquarium. Soon, however, by 
means of their pincers they tore off small fragments of the sponges, and, after first 
putting them to their mouths, placed them finally upon the dorsal surface of the 
carapace or limbs, sticking them there with a rubbing movement. Sometimes 
after several vain efforts the crab brought the fragment afresh to its maxillipedes 
and then repeats its efforts to make it adhere. The animal persevered in these 
manoeuvres until the piece of sponge remained fixed in the spot where it wished 
to place it. By continuing to act in this fashion the crab succeeded in com¬ 
pletely changing its appearance, and in rendering itself indistinguishable amongst 
the objects that surrounded it. The crab proceeded in exactly the same 
fashion when the bottom of the aquarium was strewn with seaweeds or any 
kind of zoophytes. Moreover, it was observed that some specimens, clothed with 
seaweed, which were left in an aquarium of which the bottom was covered 
with sponges did not hesitate to take off their old clothing and put on a new 
one of sponges. 
The present tribe also contains the family Parthenopidce, the species of which, 
although not armed with spines and hooked hairs for holding foreign objects, 
are yet protected in the midst of their surroundings, by having the carapace 
covered with pits and variously shaped depressions, giving it a roughened corroded 
appearance, and consequently imparting a resemblance to pieces of rock or 
fragments of dead coral. 
The sharp-nosed crabs, forming the tribe Oxystomata, are so called because the 
carapace is produced in front into a short beak-like prominence, while the external 
maxillipedes which cover the mouth are narrowed and pointed at the apex. The 
families belonging to this group present great diversity of structure and habits, 
the Matutidce being active swimmers and resembling the Portunidce in having 
their posterior legs transformed into flattened paddles, while the Calappidce, which 
