REPORT ON THE PTEROPODA. 63 



B. Geographical Distribution of the Genera. 



1. The genus Dexiobranchsea is found in the Atlantic (north of the equator) in the 

 Mediterranean Sea, and in the North and South-East Pacific Ocean. 



Among the five known species, two inhabit the North Atlantic province, near the 

 west coast of the Old Continent ; two inhabit the South-East Pacific province, on the 

 west coast of the New Continent ; the fifth species lives in the North Pacific. 



2. The genus Spongiobranchsea inhabits the whole Antarctic province, all round 

 the South Pole, where its single species seems quite to correspond to Clione limacina 

 of the Arctic province. Like this last species, indeed, Spongiobranchsea australis never 

 passes the limit of floating ice, and its area of distribution is enclosed within the isotherm 

 of 50° F. for August. 



3. The genus Pneumonoderma, which most abounds in species, is also the genus 

 which has the widest area of distribution. It was observed in the whole Atlantic Ocean 

 between lat. 45° N. and lat. 38° S., in the Mediterranean Sea, in the Indian Ocean, and 

 in the Pacific Ocean from lat. 58° N. to lat. 42° S. 



In the Atlantic Ocean, Pneumonoderma violaceum is hardly found south of the 

 equator ; Pneumonoderma peroni, in the Atlantic, is never found north of the tropic of 

 Capricorn ; it also lives in the Indian Ocean and Australasian provinces, always south of 

 the equator. 



In the Pacific Ocean, Pneumonoderma pacificum and Pneumonoderma souleyeti are 

 localised in the North Hemisphere, and Pneumonoderma boasi in the South Hemisphere. 



Some species, as Pneumonoderma peroni and Pneumonoderma mediterraneum, seem 

 to be very widely dispersed (the former in the South Hemisphere, the latter in the 

 Northern). This genus, however, requires fresh study when new and more abundant 

 material has been accumulated. 



4. The genus Clionopsis is only distributed in the North Hemisphere — North- West 

 Atlantic Ocean, Mediterranean Sea, China Sea and North Pacific Ocean. 



5. The genus Notobranchsea was observed in both hemispheres, both in the Atlantic 

 and Pacific Oceans. 



6. The genus Clione (with the exception of the badly known species that Bruguiere 

 found at Madagascar) is distributed throughout the whole Arctic province (the area of 

 dispersion of Clione limacina exactly corresponds with this province), the North Atlantic 

 Ocean, the Mediterranean Sea and the South- West Pacific Ocean. 



7. The genus Halopsyche has been observed in the whole of the West Pacific Ocean, 

 north and south of the equator. 



The following table summarises the description given above of the geographical 

 distribution of the genera of Gymnosomatous Pteropoda (this table only gives the 



