246 bulletin: museum of compakative 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 Physaha, 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. Tlie 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 smalluess 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 



