INTRODUCTORY REMARKS. 
TueE collection dealt with in the present paper is extremely large, both 
as to the number of species, sixty-three, and especially as to the numbers of 
the specimens of the major part of the forms. A small portion of the material 
was captured by the late Alexander Agassiz near the Fiji Islands in 1897, a still 
smaller lot was secured during the trip of the ‘“‘ Albatross” in 1899-1900, but 
the vast majority has been collected by Dr. Agassiz in 1904-1905 in the Eastern 
Pacific. When we wish to get a closer insight into the whole topic it is, how- 
ever, necessary to consider separately the two orders still not infrequently 
united under the name Schizopoda, viz. Mysidacea and Euphausiacea. And a 
comparison with the results of the exploration of the Dutch “Siboga” Expedi- 
tion in the Indian Archipelago is interesting. 
Of the order Mysidacea only twenty-three species are at hand, fifteen of 
which were secured in 1904-1905, while the remaining eight forms were exclu- 
sively gathered during the earlier trips just mentioned. Fifteen species in all 
from the Expedition in 1904-1905 is in reality a small number as compared with 
the number of species already known of this order. But the explanation of this 
fact is given below, and when we consider the order Euphausiacea the aspect 
is quite different. Of the last-named order the collection contains forty species, 
all with a single exception taken in 1904-1905 (some among them besides in 
1899-1900 or off the Fiji Islands), but as only seventy-three species of this order 
are known from all seas, it will be seen that Dr. Agassiz during that single 
Expedition captured more than half of the world’s fauna. The ‘“‘Siboga” 
gathered only twenty-five species of Euphausiacea but no less than forty-seven 
species of Mysidacea. The explanation of this startling difference between the 
" results of the Agassiz Expedition of 1904-1905 and the “Siboga” Cruise is that 
the Euphausiacea are nearly all true oceanic forms, while the majority of the 
‘Mysidacea either inhabit shallow water, or live pelagically, or not far from the 
bottom to a few hundred fathoms and within no very great distance from land. 
And while the “Siboga” in the main explored the straits and comparatively 
