CHARACTERISTIC DEEP-SEA TYPES. — CRUSTACEA. 41 
at both ends. To adapt it to its peculiar dwelling, the posterior 
rings of the tail are formed into a large and bilaterally sym- 
metrical operculum of calcified plates, which closes the poste- 
rior opening as effectively as the stout claw does the anterior. 
The animal is straight, and has not the curved abdomen of the 
hermit-crabs ; it enters its abode, not backwards, as do the her- 
mit-crabs, but forwards, head first. Mixtopagurus paradoxus 
has a slightly asymmetrical tail, in which the rings are more 
or less distinct, but not completely calcified, so that it is inter- 
mediate in this respect between Pylocheles and the typical her- 
mit-crabs. All three of these remarkable forms were taken in 
100 to 200 fathoms in the West Indian region. 
The species of Catapagurus inhabit depths of 50 to 300 
fathoms from the southern coast of New England to the West 
Indies, and live in 
a great variety of 
houses which only 
imperfectly cover the 
animal, of which 34% 
the front portion of # 
the carapace is in- 
durated. They are 
often associated with 
a colony of polyps, 
Epizoanthus (Fig. 
235), or the house 
is built up by the 
base of a simple 
polyp, 4damsia, which has expanded laterally and united below 
so as to enclose the crab in a broad cavity. (Fig. 236.) The 
houses are generally built upon fragments of pteropod shells or 
worm-tubes as a nucleus. This is frequently resorbed. 
The Epizoanthus houses are very often disproportionately 
large for the crabs inhabiting them, having grown out on 
either side until they are several times broader than long. 
In spite of these enormous houses, both species of the genus 
probably swim about by means of the ciliated fringes of the 
ambulatory legs. A similar cooperative association between a 
WV, 
Fig. 235. — Catapagurus Sharreri. 2, (S. I. Smith.) 
g 1 
