VI OXYRHYNCHA—CATOMETOPA 193 
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. Jnachus, Pisa, 
Hyas, Stenorhynchus, Maia, Eneepha- 
loides (Fig. 132). 
Fam. 2. Parthenopidae. — The 
chelipedes are much larger than Fie. 132.— Kneephaloides arm- 
strongi, x 1. The long walk- 
Piewtouher) legss | SOrbits, complete” 9s) ices are omitted. GC, Great 
Lambrus (Fig. 135), Parthenope. chela ; G, one of the greatly 
swollen gill-chambers. (After 
Fam. 3. Hymenosomatidae.—The —ajeock.) 
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- 
teristic of the Antarctic seas. 
Hymenosoma, Trigonoplax. 
Tribe 5. Catometopa. 
These Crabs resemble the 
Cyclometopa in general ap- 
pearance, but the carapace is 
Fic. 183.—Lambrus miersi, x 1. (After ; 5 ; j 
sony NS rery square 1n outline, an 
Milne Edwards and Bouvier. ) Needs at i a d 
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 
WOES AN O 
