696 L. A. BORRADAILE. 
the whole, however, their general shape of body, with a bent abdomen carrying good pleura, 
subeylindrical or depressed cephalothorax, and fourth pair of legs like the third rather than 
the fifth, shows a nearer kinship to the Galatheidea than to any of the other groups, and 
in the absence of any evidence to the contrary this judgment must stand. As for their 
likeness to the Raninidae among the Crabs, an admission that this indicated relationship would 
lead to great difficulties, as for instance that the Raninidae must either be removed from 
the closely related Oxystomes or the latter be supposed to be derived by modification from 
the highly specialised Hippidea—in itself a very unlikely speculation. 
Each of the above groups has its peculiar habits and habitat. The Galatheidea hide 
under stones or dwell in weed. The Thalassinidea generally make burrows, but the more 
primitive genera among them show a tendency to shelter in weed or sponges. The Paguridea 
(except Lithodinea) place their abdomen in the hollow of some foreign body, which is usually 
a gastropod shell, but in the primitive genera may be a stone or a sponge. The Hippidea 
bury themselves in the sand. Of these habits, that of the Galatheidea is the least specialised 
and could easily have given rise to the others. 
We are now in a position to sum up in the form of a tree the results reached in this 
and former articles (Pl. XLVIII.). When this is done two facts of importance appear. First 
that the proper place of the Thalassinidea is in the midst of the anomurous groups, and 
that they must no longer be classed with the Macrura, and secondly that, when this change 
is made, the Anomura, like the Brachyura, become a true, monophyletic group. Thus the 
reptant decapods fall into three divisions, Brachyura, Anomura’ and Macrura. To the subject 
of the taxonomic value of these groups and their relation to the natant families I hope to 
return later on. For the present they may be called suborders’. 
The following keys give more precisely the classification of the groups discussed above : 
Key to the reptant suborders of the Decapoda. 
I. 3rd pair of legs like the first, either chelate or simple and subcylindrical. Abdomen macrurous 
(straight, symmetrical, well armoured, with good pleura and strong, broad tail-fin, a lobe on 
the first segment clipping the carapace). Gnathobase of 2nd maxilla narrow. Basipoditic lobe 
of lst maxilliped usually deep. Exopodites of maxillipeds with lash directed forwards. Gills 
numerous. [Last thoracic segment with legs not differing greatly from the rest and sternum 
rarely free. | Macrura. 
II. 3rd pair of legs unlike the first’, never chelate. Abdomen rarely macrurous. Gnathobase of 
2nd maxilla typically broad. Basipoditic lobe of Ist maxilliped broad but shallow, its inner 
edge in a line with that of the coxopodite. Exopodites of maxillipeds with lash, when present, 
nearly always bent inwards. Gills usually few. Last thoracic segment with limbs often differing 
greatly from the rest and sternum free or not. 
1. Carapace not fused with epistome. Last thoracic sternum free, its legs differing always clearly 
in size and position and nearly always in shape from the third pair. Abdomen anomurous 
(reduced in some of its features but showing clear traces of some other function than that 
of reproduction and almost always carrying biramous limbs on the 6th segment) or, rarely, 
1 Unlike Boas’ term ‘‘ Anomala,” the name ‘‘Anomura” which it has not had before. 
has had yery different meanings in the pages of different 2 The Brachyura is ranked lower on p. 427. 
writers. This fact allows it to be used here with a denotation 3 See footnote to p. 693. 
