246 BULLETIN: MUSEUM OF COMPARATIVE -ZOOLOGY. 
every station, and in every haul; but the inside hauls were uniformly 
much more productive than those made at sea. This is probably in 
large measure due to the fact that the former were always made at 
about nine o’clock in the evening, an hour which seems particularly 
favorable for Medusae to come to the surface, and when the water was 
always very calm. The surface of the ocean itself was usually rather 
barren during the daytime; but on one occasion, on January 19, 
while we were sounding to the eastward of Guradu island, we found 
it very rich, taking Physalia, Porpita, Cestus, Aurelia, Oceania, Aglaura, 
and swarms of Copepods, Amphipods, Pteropods, and Heteropods. 
The small number of our outside hauls makes it impossible to draw 
any comparison, between the Medusa fauna of the lagoons and of the 
open sea, more comprehensive than the following correlation between the 
open character of the atolls, with their free circulation of water, and 
the fact that there was no Trachomedusa which we took outside, and did 
not take commonly inside as well. Of the nineteen species of Hydro- 
medusae which we collected, eleven were Leptolinae, and eight Trachy- 
linae, a proportion of Trachyline forms which at first sight seems large, 
considering that by far the greater number of hauls were made in shallow, 
enclosed waters within the lagoons. The explanation for this condition 
again is found in the free circulation through the atolls, which is 
constantly sweeping the adjacent surface water of the ocean through 
them to an unusual degree. 
We took in all sixteen genera of Hydromedusae, two of Scypho- 
medusae, three of Siphonophorae and four of Ctenophorae, making a 
total of twenty-five genera, represented by twenty-nine species: of 
these one genus and fifteen species are new: nine species are already 
known, while four, represented each by a single specimen, were too 
fragmentary for determination. The number of Siphonophores, when 
compared with similar collections from other tropical waters, is sur- 
prisingly small. That so few of the species known to occur off the 
coast of Ceylon (Haeckel, Siphonophorae of the “Challenger” Expedi- 
tion) exist also in the Maldives is very improbable, and the smallness of 
our catch must be attributed to some other cause. 
The distribution of the fifteen new species is as follows: of the 
eleven Leptolinae, all, with one possible exception (Dipurena), are new ; 
of the eight Trachylinae four are new; of the two Discomedusae, one ; 
and of the four Ctenophorae, all, with one possible exception, are new. 
All of the Siphonophores belong to well-known and widely distributed 
species. The geographical occurrence of the nine known species is 
