3. Implicitly it has been taken for certain by all 

 authors that the presence or absence of a spiniform dorsal 

 process from the hind margin of third abdominal segment 

 in Euphausia, etc., is an excellent specific character. But 

 later in this treatise it is shown, that all specimens of 

 E. similis G. O. S. mentioned in the literature and those 

 from several localities in three oceans seen by me have no 

 such process, while all my 1 1 specimens from four locali- 

 ties extremely distant from each other have a well deve- 

 loped, compressed process continued forward as a short 

 keel. This seems thus to be variation of local nature, but 

 certainly it originates in places very distant from each 

 other, and from one locality the adult specimens are small, 

 from another very large. A somewhat similar, but less 

 pronounced case has been observed by Tattersall and later 

 by myself in E. Vallentini Stebb., which generally pos- 

 sesses an extremely thin process from the third segment, 

 and this process is easily broken off, but in some speci- 

 mens it has seemingly not been developed. 



4. Among the numerous species found both in the 

 Atlantic and the Pacific and besides not infrequently 

 known from the Indian Ocean only three or four show 

 any appreciable geographical variation. The variation in 

 Thysanopoda pectinata Ortm. is mentioned below. And the 

 most peculiar variation of this kind is found in two species 

 of Nematoscelis. Adult males of N. mi crops G. O. S. and 

 N. tenella G. O. S. from the North Atlantic have a distinct 

 denticle posteriorly on the lower margin of the carapace, 

 but in males from the East Pacific this denticle is wanting, 

 while it is found in males from the Indian Archipelago, 

 though in N. tenella from this area it is very small. Fur- 

 thermore the rostrum of both sexes of N. microps shows 

 both purely individual and distinctly geographical varia- 

 tion, as mentioned in the « Siboga » report. 



(210) 



