250 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Section III. BRACHYURA. 
The True Crabs. 
The Brachyura represent the most highly specialised form of Crustacea. 
Swimming habits have practically been abandoned, and the diminished 
abdomen is permanently turned under the thorax. Armouring is usually 
fairly heavy, and the crab sees a fight to a finish instead of escaping at 
the expense of a leg. 
The most easily procurable types in the Clyde are Garcinus moenas 
(Penn.) (the green shore crab). Cancer pagurus, Lin. (the edible crab), 
Portunus puber (Lin.) (the swimmer crab), Hyas araneus (Lin.) (the 
spider crab), and Inachus dorsettensis (Penn.) (the slender spider). It 
was on the first four types that the majority of the observations were 
made, but the more rare forms were also examined. 
Garcinus mcrnas may be got beneath almost every weed-covered stone 
on a rocky shore, and is remarkable for the extent to which it loses its 
legs. The following tables show the percentage : — 
Crabs collected at Cullercoats, Northumberland, January 1915. 
Number, 
Carapace. 
Number with 
Legs Missing. 
Per cent. 
Total Loss 
of Legs. 
Average Loss 
per Crab. 
37 
cm. 
ov^er 5^ 
18 
48-6 
36 
2 
29 
over 4 
7 
24-1 
9 
1*2 
40 
under 4 
9 
22-5 
10 
IT 
Crabs collected at Lion Rock, Cumbrae, March 1913. 
Number. 
Carapace. 
Number with 
Legs Missing. 
1 
1 
Per cent. ' 
1 
cm. 
22 
4i-3i 
11 
50 
26 
14 
3J-2* 
21-3 
6 
4 
23 
28 
13 
2‘'-ll 
0 
0 
The above crabs were collected from rocky shores, and the liability to 
injury is seen to vary directly with the size, loss of limbs being present in 
about 50 per cent, of crabs three years old and upwards. 
If collections are made on sandy beaches at the same season of the 
