88 



MEDUSA. I. 



north coast or iii the fjords of the north-western part of tlie country. As the species lives at the Bri- 

 tish, Norwegian, and Danish coasts, one should also expect it to occur at tlie southern and western 

 coasts of Iceland and not to be restricted to the north coast, where the water is distinctly colder. By 

 a more thorough examination of the facts we ma\-, however, find a natural, though hypothetical, ex- 

 planation of the fact here mentioned. First we must pay attention to the currents around the Icelandic 

 coasts. The northern branch of the Gulf Stream runs towards the south coast of Iceland and turns in 

 a westerly direction (the Irminger Current), running towards the west along the south coast, towards 

 the north along the west coast, and towards the east along the north coast, its power and effects 

 gradually decreasing. The Polar Current, coming from the Polar Sea, strikes the north-east point of 

 Iceland (Cape Langenses) and divides into two branches; the left branch runs towards the south along 

 the east coast of Iceland, meeting the above mentioned northern branch of the Gulf Stream over the 

 Wyville Thomson ridge; thereby the warm current is forced towards the west, the cold current towards 

 the east; there may be an extraordinaryly sharp limit between the warm and the cold water near the 

 i.sland Papey on the south-east coast of Iceland. The right branch of the Polar Current bends towards 

 the west, but meets the comparativel\- warm coastal current and is forced, therefore, to run in some 

 distance from the coast in a direction towards the east coast of Greenland, where it unites with the 

 East-Greenland Polar Current. The distance of the cold water from the north coast of Iceland varies 

 very much according to tlie season and other circumstances, but during the summer the warm current 

 has usually so much power that the coastal water is comparatively warm all along the north coast 

 as far as Langenaes. There is nothing particular, therefore, in the boreal species Tiaropsis umlticirrata 

 being able to live in the fjords of the northern coasts of Iceland, and it is quite natural that the 

 species is entirely wanting on the cold east coast; but why has it never been found at the west and 

 south coasts? Now we must remember that in the British and adjacent waters the species has its 

 occurrence in the spring, the young medusEe appearing in Marcli — April, reaching maturit>' in May. 

 Undoubtedly young Tiaropsis might also be found at the south and west coast of Iceland in the 

 spring months, but no collections ha\e been made in Icelandic waters during that season. My hypo- 

 thesis is, that the meduStC which are deliberated on the south and west coast are carried along by 

 the coastal current to the north coast, wliere they come at rest in the numerous fjords together with 

 individuals, hatched and developed on the spot; thus the want of material of the species from the 

 south and west coast is due partl\- to want of collections from the spring time, partU- to the compara- 

 tively strong current running along these coasts. The finds from the northern coasts of Iceland have 

 been made between June ist and August 12th. There are a number of young specimens, 2 — 9 mm 

 wide, from the first days of June, whereas larger individuals have been found during the later half- 

 l)art of June, and mature .specimens at the end of June, during July, and at the beginning of August. 



The -specimens, niciitioued by Bigelow, from the northern Pacific (Dutch Harbour and Agattu 

 I.sland) were found on May 25th and June 7th; they were altogether well-sized individiud.s. 



We nia\- then state as a general result that Tiaropsis iiii(lticirrata is a neritic-boreal species, 

 living in the boreal coastal regions in the North Atlantic area and in the northern Pacific. In the 

 greater part of the area of distribution its occurrence is limited to the spring months, the young 

 specimens appearing in March, growing to maturity in May, and disappearing in May or June. In the 



