THE LAND CRAYFISHES OF AUSTRALIA. 117 



Thus, in one series of f oi-ms, E. fossor. affi)iis, victoriensis, phyllo- 

 cercus, fultoni, and hemioirratidus, the exopodite of the third 

 maxillipede may be rudimentary or entirely suppressed ; in 

 another series the outer fiageUum of the first antenna is absent 

 {E. hemicirrafulus), while the antennary scale and the uropods 

 undergo striking changes in certain species. 



It is difficult to find the reason for these marked aberrations of 

 structure, but it may be pointed out that all of them are in the 

 nature of losses or suppressions, e. g. the loss of the pleurobranch, 

 the loss of the exopodite of the third maxillipede, the loss of a 

 flagellum on the antennule, the reduction of the antennary scale, 

 and the abortion of the eyes ; and it may be plausibly argued that 

 the underground, burrowing habit which removes the animal 

 from active competition with other water forms has permitted 

 degenerative changes which have no special adaptive meanings.^ 



Another interesting point is the extraordinary variability of the 

 large chelse in these forms, and their frequent asymmetry. It 

 appears to us extremely doubtful whether these variations 

 indicate specific or only individual differences, since hardly two 

 forms coming from the same locality and identical in other 

 respects are ever quite alike in regard to their chelse, and very 

 often they differ fundamentally in this respect, independently of 

 sex and size. 



Unfortunately, we do not know very much about the habits of 

 these burrowing crayfish, and the only personal observations were 

 made by one of us in Tasmania on the smaller Tasmanian Etigceus, 

 E. fosaor. 



This species is widely distributed in Tasmania, being found on 

 the southern mountain ranges, on the north coast, and in the 

 forests on the west coast. The burrows of the animal could be 

 recognised as little round holes in the damp ground, sometimes 

 near the banks of a stream or water-course, but very frequently 

 far removed from any water in the middle of the forest in some 

 damp situation. The burrow descends vertically into the ground, 

 or if it is in a bank it is frequently horizontal, and after passing 

 inwards for a foot or two it ends in a circular chamber which is 

 always full of water. Engaus foasor, when freshly taken from its 

 burrow, has a rather soft whitish skin with brilliant blue patches 

 and an occasional tinge of red. In one place near the Magnet 

 Mine on the west coast of Tasmania, the banks of an artificial 

 water-course which was used in the mining operations were com- 

 pletely riddled by the burrows of Engceus fossor, and the foreman 

 of the mine told me that these creatures were a source of continual 

 damage and danger in works of this kind. 



It is stated in Erichson's original memoir, on the authority of 

 Herr Schayer, who collected the specimens, that Engcms if kept in 

 water soon dies. In view of the fact that there is always water 

 at the bottom of the burrows, and also from what I have heard 

 from people in Tasmania who have kept the animals in captivity, 

 this statement may be received with some scepticism. 



