OXYRHYNCHA CATOMETOPA 



193 



132. — Encsphaloides arm- 

 stroiigi, X 1. The long walk- 

 ing legs are omitted. C, Great 

 chela ; G, one of the greatly 

 swollen gill - thambers. (After 

 Alcock.) 



the gill-chambers (G) greatly swollen and enlarged to make up 



for the scarcity of oxygen in these 



deep regions. 



Fam. 1. Maiidae. — The chelipedes 



are not much larger than the other 



legs, but are very mobile. Orbits 



incomplete. A very large family, 



including all the true Spider-crabs, 



very common in the Atlantic and 



Mediterranean littoral. Inachus, Pisa, 



Hi/as, Stenorhijnchus, Maia, Encepha- 



loides (Fig. 132). 



Fam. 2. Parthenopidae. — The 



chelipedes are much larger than Fig. 



the other legs. Orbits complete. 



Lamhrus (Fig. 133), Parthenope. 

 Fam. 3. Hymenosomatidae. — The 



carapace is thin and flat ; the cheli- 

 pedes are neither very long nor especially mobile. There are no 



orbits, and the male openings 



are on the sternum. Charac- 



>!^>^^SBi!i..^l "'^%, V, teristic of the Antarctic seas. 



Hymenosoma, Trigonoplax. 



Tribe 5. Catometopa. 



These Crabs resemble the 

 Cyclometopa in general ap- 

 pearance, but the carapace is 

 very square in outline, and 

 its margins are never so well 

 provided with spines as in the Cyclometopa. The position of 

 the male genital openings is peculiar, since they lie upon the 

 sternum, and are connected with the copulatory appendages 

 upon the abdomen by means of furrows excavated in the 

 sternum. The Catometopa are either littoral or shallow water 

 forms, or else they live entirely on land. The Grapsidae are 

 marine Crabs, Pachygrapsus marmoratus (Fig. 134) at Naples 

 being exceedingly common on rocks at high-water mark, over 

 which it scuttles at a great rate ; in the Mediterranean it takes 



VOL. IV 



Fig. 133. — Lamhrus miersi, x 1. (After 

 Milne Edwards and Bouvier. ) 



