MARINE CRUSTACEANS. 429 



p. Last pair of legs not dorsally placed nor markedly weaker than the rest. [Inter- 

 antennular septum not very thin e.xcept in Macrophthalminae.] 



i. A gap of greater or less size is left between the 3rd pair of maxillipeds. Front 

 broad, or moderately so. 



a. Sides of the body either straight or very slightly arched. Shape square. Rarely 

 true land-crabs. Grapsidae'. 



f3. Sides of the body arched. Shape transversely oval. Land crabs. Gecarcinidae. 



ii. 3rd pair of maxillipeds almost or quite close to the mouth. Front moderately or very 

 narrow. Ocypodidae. 



Subfamilies of the Atelecyclidae. 



I. Antennal flagella absent. [Mouth covered by 3rd maxillipeds. Front uncleft.] Acanthocyclinae. 



II. Antennal flagella present. 



A. Regions not defined. 3rd maxillipeds cover the mouth. Front entire or lobed. Thiinae. 



B. Regions more or less clearly marked out. 3rd maxillipeds do not cover the mouth. Front 

 toothed. Atelecyclinae. 



Subfamilies of the Cancridae. 



I. Carapace broadly oval. Epistome not sunken. Cancrinae. 



II. Carapace hexagonal. Epistome sunken. Pirimelinae. 



V. THE CRABS OF THE CATOMETOPE FAMILIES. 



The group Catometopa was as hard to characterise bionomically as it was to separate 

 morphologically from the Cyclometopa. The one thing that could be said about it in this 

 respect was that the bulk of its members lived, not in the sea, but on land, in fresh water 

 or between tidemarks. At the same time a considerable number were strictly marine, espe- 

 cially the Xanthid-like family Gonoplacidae and the Mussel-Crabs of the Pinnotheridae. 

 The land forms have been already enumerated above (Pt. I. p. 64) where some remarks on 

 their habits will be found. Of the others, the only genera to which any striking bionomic 

 interest attaches are Plagusia and Leioloplms, which live between tidemarks and are very 

 active (see p. 432), Pinnotheres, which inhabits bivalve shells, and Planes, found on floating 

 objects at sea. Gaecopilumnus described with the Xanthidae, etc. (p. 267), belongs, I think, 

 to the Gonoplacidae. Platyozius described in the same paper is more nearly related to 

 Pilumnoplax than to Pseudozius but is a Xanthid, as is also Pilumnoplax. 



All the species which are not new have already been described from the Indo-Pacific 

 region, most of them being Indian. The following list enumerates the species: 



' A key to the subfamilies and genera of the Grapsidae is paper {Journ. As. Soc. Bengal, Lxix. ii. 1900). The points in 



given by Kingsley (Proc, Ac. Pkitad. 1880), and the members which tlie arrangement in tliis paper differs from Major 



of most other groups of the old Catometopa can be fairly Alcock's are mostly small and will cause no confusion. 

 easily recognised by means of the diagnoses in Major Alcock's 



55—2 



