CONTENTS. 



Introduction, . 



1. History of the Group, . 



2. The Gymnosomata and their Distinction from the Thecosomata 



3. The Habits of the Gymnosomata, 



4. The Gymnosomata of the Challenger Expedition, 



Description op Genera and Species, . 



The Genera and Families of Gymnosomata, 

 Family I. Pneumonoderniatidae, 

 Dexiobranchsea, Boas, 

 ciliata, Gegenbaur, 

 minuta, n. sp., 

 simplex, Boas, 

 paucidens, Boas, 

 polycotyla, Boas, 

 Spongiobranchsea, d'Orbigny, 



australis, d'Orbigny, 

 Pneumonoderma, Cuvier, 



mediterraneum, van Beneden, 

 violaceum, d'Orbigny 

 peroni, Lamarck, 

 boasi, n. sp., 

 pacificum, Dall, 

 souleyeti, n. sp., 

 Family II. Clionopsidas, 

 Clionopsis, Troschel, 

 hrohni, Troschel, 

 grandis, Boas, 

 modesta, n. sp., 

 Family III. Notobranchaidae, 

 Notobrandima, Pelseneer, 

 macdonaldi, Pelseneer, 

 inopinata, n. sp., 

 Family IV. Clionidse, 

 Clione, Pallas, 



limaeina, Phipps, 

 longicaudata, Souleyet, 

 flavescens, Gegenbaur, 



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