NOTES ON CERTAIN SHORE GRABS. 311 
somewhat haphazard, and though there is in every case a 
clearly defined pathway, it is not so well defined as with the 
Scopimera crabs. 
There is another phenomenon amongst these Dotilla crabs 
which is worthy of mention. As is usual, on the stretches 
of shore which are exposed at low tide some parts are 
quite dry, whereas others are comparatively wet during the 
whole period of low tide. These animals appear to have 
adapted themselves to both these conditions. Some live, 
as above described, in burrows in dry sand, while others of 
the same species live on the wet patches. If such a wet-sand 
colony be cautiously approached, troops of these crabs may 
be seen moving about and feeding. When disturbed, they 
do not scurry away, as Ocypodes do, and having no ready- 
made burrows, they cannot escape as their dry-sand brethren 
do. Their method is to move to a soft wet patch of sand, if 
not already there, and then to vanish. This disappearance is 
is at first sight very astounding, as it only takes a few seconds 
for a whole colony of them to pass out of sight and leave 
the sand looking almost undisturbed. On closer examina- 
tion the mystery is explained, when one of them is seen 
disappearing down into the sand by a kind of corkscrew 
movement. The animal accomplishes this by digging itself 
sideways and downwards into the sand. This method of 
taking cover is only used for temporary escape ; for the crabs 
may be unearthed by disturbing the surface of the sand. I 
never found one which had penetrated more than an inch 
under the sand in this way. This habit provides the easiest 
method of procuring specimens. 
When these wet-sand crabs have finished feeding, 1.e., 
when the tide is rising, they have a most ingenious way of 
providing themselves with a retreat full of air while the tide 
covers their feeding ground. In the wet sand a small cavity 
about three-quarters of an inch in diameter is excavated in 
the shape of a cup (Fig. 3). Then the crab, standing in the 
middle, starts to carry wet lumps of sand from the bottom and 
piles them on to the sides. Working very rapidly, he soon 
(that is, in 2 or 3 minutes) has a complete wet-sand ‘chamber 
enclosed and roofed in, the air inside being retained by the 
