62 Papers from the Department of Marine Biology. 
coral grew more rapidly than the crab, an inverted funnel or hollow cone 
would be formed over the crab, while, if the crab grew the faster, the margin of 
its cave-dwelling, so long as it was small, could not be exactly on a level with 
the margin of the contiguous polyp-cups. But when the crab has reached its 
full length, about seven millimétres, the polyps outgrow its funnel-shaped 
dwelling, and would no doubt soon wholly outgrow it, if it were not that they 
find a certain resistance in the current set up by the crab for breathing and in 
the movements of the creature; and this resistance is sufficient to compel the 
growth of the coral in a particular and determined direction. The two powers 
in opposition thus reach an equilibrium, and it is their reciprocal action which 
gives the funnel its characteristic form. 
“Here too, as in the former instance [Hapalocarcinus], the individual 
polyps plainly show the effects of the current. While in general the cups are 
perpendicular to the surface of the coral, in most of those which grow within 
the funnel this is not the case; they have an oblique direction upwards, and 
are most oblique where the strength of the current is greatest, 2. e., at the 
narrow bottom part of the funnel.” 
The material I have investigated comes from Minikoi and has 
already been reported upon by Borradaile (Fauna and Geography of 
the Maldives and Laccadive Archipelago, vol. 1, p. 271, Marine Crus- 
taceans, III, Xanthide and some other crabs) and referred to the 
species Cryptochirus coralliodytes Heller. They were collected by Pro- 
fessor J. Stanley Gardiner and are preserved in the Cambridge Univer- 
sity Museum of Zoology. There were three males and several females. 
The dimensions (in millimetres) were as follows: 
Smallest Largest Smallest 
female. male. male. 
Largest 
female. 
Total length \'.).: 22) 
Carapace length...... 
Carapace breadth... . 
ay: 
These measurements are very similar to those given by Heller for 
C. coralliodytes from the Red Sea. 
The notes given by Professor Gardiner are as follows: 
“A block of Leptoria tenuis, which had a large number of round holes on the 
surface up to 4 mm. across, was broken up. The holes . . . were nearly 
all found to be occupied by a symbiotic crab. The holes varied in depth 
from 1 to 30 mm., the coral being in the latter case 48 mm. thick. Nor- 
mally the animal would appear to live close to the surface, with the carapace 
as a kind of shield closing the hole. When the block becomes more or less 
dry they retreat into the bottom of the holes. . .. These commensals 
are extremely common in Leptoria from the lagoon at Minikoi, but are never 
found in specimens from the outer reef. They are rare on other corals, occa- 
sionally in massive Astreids from the lagoon at Minikoi, but not apparently 
in branching corals, fungoids, or perforate corals.” 
I examined a number of colonies in a dried condition from the col- 
lections of Professor Stanley Gardiner and Mr. Cyril Crossland. In 
