Guide to Crttstacea. 
Table-case 
No. 15. 
Podophthalmus vigil (Fig. 48) is remarkable for the great length 
of the eye-stalks, which is quite unusual among the Cyclometopa, 
and gives this Crab a curious likeness to the genus Macroph- 
thalmus among the Ocypodidae ( see Table-case No. 16). The 
resemblance, however, is quite superficial, for in this case it is the 
first of the two segments of the eye-stalk which is elongated, while 
in Macrophthalmus it is the second. 
The genus Platyonychus, of which a group of specimens is 
mounted in Wall-case No. 5, also belongs to this family. 
The Cancridac are distinguished from the preceding families by 
having the antennules folded longitudinally instead of transversely. 
Fig. 48. 
Podophthalmus vigil (reduced). [Table-case No. 15.] 
To the typical genus Cancer belongs the Edible Crab of British 
coasts, of which a large specimen is exhibited in Wall-case No. 5. 
The wide distribution of the genus is illustrated by species from the 
Azores and from New Zealand. 
The family Potamonidae ( Thelphusidae ) comprises the River- 
Crabs. In the shape of the carapace, which is generally more or 
less square, and in having the front bent downwards, these Crabs 
show some resemblance to the next Tribe, Catometopa. They are 
widely distributed in fresh waters throughout the Tropics. Potamon 
edule (better known as Thelphusa fluviatilis ) occurs in Italy and 
other parts of Southern Europe. 
The family Corystidae includes Crabs which are allied to the 
Cancridae, but have long antennae, and the third maxillipeds are 
