INTRODUCTION. 



The collection of Medusae obtained during the cruise of the "Albatross" 

 in the Eastern Tropical Pacific in 1 904-05 is to be ranked as among the more 

 important of recent years. Not only is the number of species large (72), but 

 it includes two new intermediate genera of great interest from their system- 

 atic relationships, as well as excellent examples of several previously little- 

 known genera, such as Atorella, Periphyllopsis, Aeginura, Pegantha, Halicreas, 

 Homoeonema, Sibogita, and Heterotiara. The number of new species (17) 

 may seem comparatively small, but it must be remembered that the greater 

 part of the collection consists of holoplanktonic forms, organisms now known 

 to be of general distribution in the warmer waters of all oceans. The fact 

 that the greater portion of the cruise led through an oceanic area far from 

 land no doubt explains the total absence of rhizostomes from the collection. 

 Intermediate genera, both craspedote and acraspedote, are especially well 

 represented. 



Among the features of morphologic interest I may call attention here to 

 the discovery of a new halicreid, Halitrephes, with numerous radial canals ; 

 of a new trachyneniid, Tetrorchis, with four gonads on the subumbrella ; 

 of a Cunina lacking peripheral canal system ; of a Cunoctantha, C. tenella, in 

 which, unlike previously known members of this genus, a canal system is 

 well developed ; and of the development of free medusa buds in the region of 

 the gonads in a new species of Eirene. From the developmental standpoint 

 the discovery of an almost complete series of stages in the development of 

 Pegantha smaragdina is of especial importance, since nothing was previously 

 known of the early stages of this interesting genus; and of equal importance 

 is the demonstration of the occurrence of internal budding in Cunina and 

 Pegantha. 



To the student of geographic distribution the collection is especially timely, 

 since although the explorations of the recent deep-sea expeditions of the 

 " Valdivia," the " Siboga," and those of the Prince of Monaco had given us a 

 fairly good idea of the holoplanktonic Medusa fauna of the Tropical Atlantic 



