170 PERCY SLADBN TRUST EXPEDITION 



The medusse which are known to be, or expected to be, connected with hydroids 

 may require a finer discrimination of specific characters than those which have direct 

 development. The linking together of species which very closely resemble each other 

 under a common name, but are found in localities very far apart, may lead later on to 

 further confusion and erroneous ideas on geographical distribution of marine animals. 

 We are not yet certain that hydroids which are universally recognised as distinct species 

 of a genus may not have medusae so much alike that there is the possibility of their 

 medusae being regarded as belonging to the same species. We know that hydroids 

 belonging to families far removed have medusae closely related according to our present 

 system of classification, but we do not know what surprises are in store when all the 

 hydroid species of Syncoryne, Bougainvillia, Perigonimus, Obelia, Campanulina, etc., 

 have had their medusae reared and traced to their adult stages. 



A different treatment of specific characters appears to me to be required for those 

 medusse ■which have direct development (without any hydroid stage), especially those 

 belonging to certain genera, such as Liriope and Pelagia, which are found throughout 

 the warm regions of the oceans. There are many genera which have a vast geographical 

 range, but how far their species are valid is still a debatable subject. At one time 

 a formidable list of species was being piled up, but the tendency is now to reduce the 

 species to about one per genus. I think this latter process is being carried too far, it 

 makes work easy for the systematist, but is bad for Science. It appears to me that 

 a species belonging to this class of medusae shows a far greater I'ange of variation than 

 those belonging to the Anthomedusae and Leptomedusse. We have formerly been 

 basing the specific characters upon a too limited number of specimens, and have described 

 the characters of an individual rather than those of a race. There are certainly distinct 

 races of Liriope and Pelagia, and some of them are good species. 



The following is a classified list of genera and species found on the cruise of the 

 " Sealark " : 



HYDEOMEDUS^. 



ANTHOMEDUS^. 



Euphysora higelowi, Maas. Amphinetna sp. 



Steenstrupia normani, n. sp. Leuckartiara gardineri, n. sp. 



Zanclea orientalis, n. sp. PanJcea juv. ■ 



Zanclea juv. Heterotiara minor, Vanhoffen. 



Gytceis tetrastyla, Eschscholtz. Proboscidactyla tropica, Browne. 



Bougainvillia fulva, Agassiz and Mayer. Proboscidactyla sp. 



Turritojjsis nutricula, McCrady. 



LEPTOMEDUS^. 



Tiaropsis rosea, Agassiz and Mayer. Mesonema pennile (Modeer). 



Phialidium sp. lEquorea macrodactyla (Brandt). 



Irene sp. 



