26 - 
Q) 
o 
24 
22 - 
20 “ 
18 - 
6 - 
14 “ 
w 
12 
O 
CD 
10 - 
8 - 
‘8T 
x x x 
X o 
o - P. hirsutiusculus — all shells 
* - P. gronosimanus — all shells 
# - P. samuel is — Tegula funebralis 
A - P. samuelis — Tegula brunea 
X- P. samuelis — Calliosfoma 
o a 
Width of carapace in mm. 
Fig. 4. Relationship between size of shell utilized and size of crab at Horseshoe Cove. 
brunnea shells were of suitable size and they 
consequently were preferred. Both of these spe- 
cies chose shells of a size to permit the entire 
carapace to be withdrawn until the large cheli- 
ped was in a position to act as an operculum. 
This preference is reflected in the size of shells 
utilized by the crabs in nature ( Fig. 4 ) . 
In eviction experiments, P. hirsutiusculus was 
dominated by the other two species, usually 
being evicted by crabs of the other species if 
they made such an attempt. In no case did a 
specimen of P. hirsutiusculus successfully evict 
