. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. PELAGIC ANIMAL LIFE 589 \ w Fig. 432. Cavolinia gibbosa, Ran| (From Meisenheimer/ 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. 450 or 460 N. we meet with only a few of the warm- water forms, Creseis acicula and Clio cuspidata having been taken in isolated specimen
. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. PELAGIC ANIMAL LIFE 589 \ w Fig. 432. Cavolinia gibbosa, Ran| (From Meisenheimer/ 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. 450 or 460 N. we meet with only a few of the warm- water forms, Creseis acicula and Clio cuspidata having been taken in isolated specimens up to 6o° N. Typical denizens of this region are Clio pyramidata and Diacria trispinosa, which appear to be as numerous as under the equator. The northern forms Limacina helicina 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,1 who reported on the pteropoda of the " Valdivia " Expedition, is of opinion that the horizontal and vertical distribution of the ptero- poda depends mainly on the temperature. Most of the species require a high temperature, and for this reason the majority live in the surface layers. Only exceptionally do they occur as deep as 1000 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 diversa, Lima- cina helicoides, and Clio falcata, which ^ occurred only between 500 and 1500 jffllJL metres. J| B r During the Atlantic cruise of the â "Michael Sars" pteropoda were taken in thousands, and this material has been B M examined by Bonnevie, who records the following species :â TheThecosomata include:âLimacinidae: Limacina balea, L. retroversa, L. buli- moides, L. infiata, L. lesueuri, L. helicina, L. helicoides, Peraclis reticulata, P. triacantha, P. diversa, and
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