much longer, very considerably expanded with convex 

 lateral margins and covers most of the eye-stalks, while 

 rostrum is short. Another adult female shows a feeble 

 degree of the same development. 



It is certain that these instances of strong variation are 

 not mainly, or perhaps not at all, geographical but indi- 

 vidual, and they cannot be considered as cases of acci- 

 dental deformity. Variation in the degree of development 

 of processes etc. is well known in many Amphipoda, but 

 it is frequently connected with variation in size of the 

 animals, often arising from differences in salinity or tem- 

 perature. At all events such variation cannot be compared 

 with that found it the two species of Euphausia^htVQ the 

 thing is, that in some few specimens of normal size and 

 of both sexes a single and conspicuous organ not serving 

 any appreciable purpose is developed in a quite unusual 

 way. And I am not aware that variation in any way com- 

 parable with that in the specimens of the two species of 

 Euphausia is known within any other group of Crustacea. 

 It may be added that of several other species of the same 

 genus I have determined from a hundred to some hundred 

 specimens of each species without observing a single case 

 of expansion of the frontal plate. 



2. A number of specimens of Euphausia similis G. O.S. 

 from the South Atlantic, the Indian Ocean and the Pacific 

 have the frontal plate.and rostrum developed in the nor- 

 mal way. But all three immature specimens of this species 

 from a locality in the Indian Archipelago have the frontal 

 plate with rostrum and besides the gastric area anoma- 

 lously vaulted, with the plate larger and the rostrum shor- 

 ter than in normal specimens ; the aberrant animals have 

 been described and figured in the « Siboga » report. 

 Though the general aspect of this variation is different 

 from that in E. diomedeœ, the case may be analogous, but 

 as all my specimens from that locality and area show the 

 vaulting, which is comparatively much more developed 

 in the largest than in the smallest specimen, I do not ven- 

 ture to draw any conclusion. 



