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PELAGIC ANIMAL LIFE 589 



of these warm-water species of pteropoda are also known from the 



Indian and Pacific Oceans, where their geographical distribution is 



similar to that in the Atlantic. North of lat. 45" 



or 46° N. we meet with only a few of the warm- ,/y'^^^~~'^: 



water forms, Creseis acicula and Clio cuspidata 



having been taken in isolated specimens up to \ 



60° N. Typical denizens of this region are Clio / ^ 



pyraniidata and Diacria trispinosa, which appear ' 



to be as numerous as under the equator. The 



northern forms Liviacina lielicina and L. balea, as 



well as Clione limacina, also occur in the northern 



part of the Atlantic. In the Antarctic we find 



species which are very similar to the northern 



ones. 



Meisenheimer,^ who reported on the pteropoda 

 of the " Valdivia" Expedition, isof opinion that the \y 



horizontal and vertical distribution of the ptero- ^ 



poda depends mainly on the temperature. Most ^ ,. .^^^'.^}'^' ^ 



^,. ^. . 1-1, , ir Cavohma ginbosa. Rang. 



of the species require a high temperature, and for (prom Meisenhdmer. ) 



this reason the majority live in the surface layers. 



Only exceptionally do they occur as deep as lOOO metres, and this is 



specially the case in the Mediterranean, where high temperatures prevail 



to very considerable depths. During 

 our Atlantic cruise we found some real 

 deep-sea forms : Peraclis diver sa^ Lima- 

 cina helicoides, and Clio falcata, which 

 occurred only between 500 and 1500 

 metres. 



During the Atlantic cruise of the 

 " Michael Sars " pteropoda were taken 

 in thousands, and this material has been 

 examined by Bonnevie, who records the 

 following species : — 



The Thecosomata include: — Limacinidse: 

 Limacina balea, L. retroversa, L. buli- 

 moides, L. infiata, L. lesueuri, L. helicina, 

 L. helicoides, Peraclis reticulata, P. triacanfha, 

 P. diversa, and Procymbulia sp. Cavolinidae: 

 Clio pyraniidata, C. cuspidata, C. falcata, 

 Creseis acicula, Sty Ho la subula, Hyalocylix 

 striata, Cuvierina columnella, Diacria tri- 

 spinosa, D. quadridefitata, Cavolinia infiexa, 

 C. gibbosa, C. loigirostris, C. tridentata. 

 Fig. 433. C. uncinata. Cymbulidse : Cymbulia 



Clione limacina, Ph'\^Y>^. (FromlVanhoffen.) peronii. 



The Gymnosomata comprise, besides 

 Pneumodermopsis macrochira 'and Clio/ie limacina, several new species not yet 

 described. 



Of other Mollusca I may mention the beautiful surface forms : 



^ Meisenheimer, Wiss. Ergeb. '■'■Valdivia'' Expedition, Bd. 9, 1905. 



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