SCYPHOMEDUSAE 377 



of Good Hope and west of the Cape. It is, however, not impossible that this must be 

 partially ascribed to more thorough collecting at these places. The southernmost station 

 at which A. forma bairdi and verrilli have been found is St. 391 in 55° S, 52° W. The 

 northernmost localities of A . forma wyvillei are in the Gulf of Guinea in 8° N at a depth 

 of 850-goo m. It is obvious that A. forma wyvillei only occurs in a layer of water of low 

 salinity which in the eastern basin of the Atlantic does not reach farther than 10° N. 

 In the Guinea basin this water layer of 34"5-347 7oo salinity is found at a depth of 

 500-1000 m. As A. forma wyvillei is the only form from Antarctic waters, and occurs 

 in more southern regions, especially in water of Antarctic origin, and as forma bairdi 

 and forma verrilli are typical of the northern Atlantic regions and do not occur farther 

 south than 55° S, it seems very probable that wyvillei and bairdi (the latter including 

 verrilli) are two distinct geographical forms which are co)ifined to special currents or regions 

 (cf. however, Broch, 1913, p. 16). 



Vertical distribution. As may be seen from Tables VI and VII Atolla was found 

 from the surface (200-0 m.) down to 2000-2500 m. Most specimens occur between 

 700 and 1500 m., and Atolla belongs therefore to the "intermediate fauna" of Bigelow 

 (1909, 1913). The largest number was caught at 13° 25' N, 18° 22' W (south of Cape 

 Verde) with twenty-four specimens from 900 m. upwards, the next at St. 151 in 

 1025-1275 m. in depth with nineteen specimens and the third on St. 407 with eighteen 

 specimens from 800-900 m. depth. We will now consider each form separately. 



Atolla wyvillei forma verrilli has been found at a depth of 1000 m. or more with the 

 exception of two stations, 267 and loi, where it was caught in 450-550 and 300-400 m. 

 The occurrence in more superficial layers here is perhaps due to cold upwelling 

 currents. The Valdivia Expedition (1903, p. 10) found this form at several stations on 

 the west coast of Africa from the Equator to the Cape (depth not indicated). The 

 Deutsche Siidpolar Expedition found it between Tristan d'Acunha and Cape Town, and 

 west of Cape Verde to the south of the Equator at a depth of 3000 m. (1909, p. 36). 



Atolla wyvillei forma bairdi occurs below 900 m. with the exception of the hauls at 

 Sts. 270 (Elephant Bay), 282 (Annobon Island) from 200 to 400 m. and St. 267 (Cape) 

 from 450-500 m. in regions where cold upwelling currents are present, and in a catch 

 from 650 m. at St. 81 (Tristan d'Acunha) in a layer of low salinity of 34-5 °j^^ . More 

 than half the specimens come from a depth of 800-1000 m. This form was found 

 previously by the Plankton Expedition (1892, p. 16) south of Cape Verde in 4000 m., 

 and by the Valdivia Expedition in the Guinea stream (1903, p. 10, depth not indicated). 



Atolla wyvillei forma typica is found in the upper layers in the far south, Sts. 592 and 

 595 (South Shetlands) and WS 552F (Coats Land), off the west coast of Africa at 

 Annobon Island (St. 282) in the Gulf of Guinea, north of the Cape (St. 267), and north- 

 west of the Cape (St. 407), at all of which places (besides the Antarctic localities) deep 

 water from the depths rises towards the surface. Elsewhere it occurs only in great 

 depths between 800 and 1600 m. (maxima at 1000 and 1500 m.) with the exception of 

 St. 114 near Bouvet Island, where it occurs at about 700 m. The 'Challenger' found 



