ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



PTEROPODA. 



39 



As exceptions may be mentioned the occurrence of at the same time a wedge of warm-water runs northwards 



1) the arctic species Limacina helicina within the to Station 81, where warm-water Limacinidae were taken, 

 transitional zone (Station 80); The opinion of Meisenheimer that these Limacinidae are 



2) the transitional species Limacina balea within the to be considered as stenothermal forms, occurring only 

 circumtropical zone (Station 66); and within certain temperature limits, is therefore in no way 



© Styliola subula 

 © Crescis acicula 

 %) Hiialocylix striata 



® Diacria quadridcntata 

 9 Cav. inflexa 

 (•) Cav. gibbosa 



Fig. 34. 



O Cav. tridentata 

 Q Cav. longirostris 

 Q Cav. uncinata 



3) the warm-water species Peraclls reticulata, Lima- 

 cina lesueiirii and Limacina Inflata within the transitional 

 zone (Station 81). 



A glance at the chart (textfig. 33) showing the hydro- 

 graphical conditions at depths of 200 to 500 metres at 

 the time of the expedition will, however, explain all these 

 exceptions. At this depth Station 80, where Limacina 

 helicina was found, lies within the cold zone; a wedge 

 of cold water from the transitional zone penetrates as far 

 south as to include Station 66 (Limacina balea); while 



contradicted by their appearance at latitudes beyond the 

 main boundary lines of these zones. 



Besides the stenothermal species of Limacinidae, one 

 species, Limacina retroversa Fleming, is eurythermal, for 

 although belonging to the warm-water zone it may be 

 found widely distributed in the northern transitional zone. 

 The two deep-sea species Peraclls dlversa and Limacina 

 hellcoldes will be considered later. 



Most of the species of Cavoliniidae are, according 

 to Meisenheimer, stenothermal warm-water species, while 



