SCIIIZOrOPA. 3 



said to have reached that state. Still, they afford material for a re-description and 

 figures of the species in the adult state, with some notes on the growth changes. 



The Mysidacea consist of eleven specimens, referaljle to six species. The most 

 interesting of these species is Hansenomysis antarctica, au Antarctic representative of 

 a genus hitherto known from hut three specimens from Arctic and boreal waters. 



The chief interest of the collection lies in the evidence which it may afford as to 

 the similarity or dissimilarity of the fauna at the two poles. There are no species 

 common to the fauna of l)oth polar regions in the collection ; l)ut, on the other hand, 

 all the genera save one, Antarctomysis, are represented in northern waters by species 

 which are cjuite distinct from their southern allies. 



Exploration of the bottom fauna of the deep waters of the globe, especially in 

 tropical and sub-tropical regions, is as yet only in its infancy, and it is therefore 

 extremely proba1)le that what are now known to be bipolar genera and species will in 

 future be found to be cosmopolitan in their distribution. The Schizopoda were long 

 thought to have in Lopliognster typicus a stock instance of a bipolar form, but the 

 gaps in its distribution have been almost completely filled up as a result of recent deep- 

 sea work, and, with the exception of the tropical Atlantic, its range is known to be 

 complete from Norway to the Cape. 



Two bipolar species of INIysidse are known, however — Boreomysis myphops, G. 0. 

 Sars, from Arctic waters, and Lat. 50° S., near the Crozet Islands, and Ambiyops 

 crozefti, from the seas of Greenland and Ian May en in the north and the Crozet Islands 

 in tlie south. They are not known from the intermediate waters. 



Of the genera of Antarctic Schizopoda, Euphaiisia, Thysanoessa, and Eucupia. are 

 world-wide in range, but the northern and southern species are quite distinct, even the 

 hitherto supposedly cosmopolitan Eacopia australis, Hansen having shown to contain 

 at least two species, probably three. 



Pi^eudomma, Hansenomysis, Dactylamhlyops, and Mysidetes are, as at present 

 known, bipolar genera, but Pseudoniiwi, at least, ranges far from both poles, and 

 further exploration will probably extend the known range of the other genera also. 



The most interesting case is presented by the genus Antarctomysis. It is closely 

 related in structure to the northern species Michtheiniysis mixta (Lilljeljorg), a .species 

 inhabiting chiefly the colder waters of the northern hemisphere. The two genera are 

 separated only in the characters of the male pleopods, which are more primitive in the 

 Antarctic form, and neither genus is likely to be found to have a distribution which 

 extends very far from the poles they frequent. 



In the preparation of this report 1 have received much valuable help from many 

 sources. The authorities of the British Museum kindly allowed me to examine and 

 dissect two specimens from the ' Challenger ' collections in their charge. To Dr. 

 Caiman, of the British Museum, I have been much indebted for information on many 

 points connected with the 'Challenger' material, and he lias, also, at my rc(|nest, 

 funiishcd me with drawings of various species. Mr. E. \V. L. llolr kimlN' examined 



