•2 THE VOYAGE OF H.M.S. CHALLENGER. 



Tliis difference in tlic distribution of those allied genera seems to be associated with 

 dilierences in temperature. The eighteen known species of Pkymosoma are almost 

 exclusively tropical or subtropical forms,^ occurring only at moderate depths or near 

 shore, and therefore in water comparatively warm. Now, since the temperature of the 

 deep sea is on the whole strikingly low, the almost total absence of forms of Phymosoma 

 in these depths may l^e conditioned by the lack of the requisite warmth. On the other 

 hand, the great majority of the tube-inhabiting forms belonging to the genera Phasco- 

 losoma and Phascolion were found in the waters of the temperate and cold zones, and in 

 the deep sea, while several species of the same genera are also tropical. 



In describing the various species I have given references to the more important 

 literature of the subject. In regard especially to the Gephyrea achceta, I would mention 

 my recent monograph on the Sipunculi.'^ 



Sy7topsis of the Genera and Species. 



A. Gephyrea ch^tifera. 



Genus 1. Steniaspis, Otto. 



1. Sternaspis princeps, n. sp. 



Genus 2. EcMurus, Gueriu. 



2. Echiurus unicinchis, v. Drasche. 



Genus 3. ThaJassema, Gaertner. 



3. Thalassema faex, n. sp. 



4. Thalassema haronii, Greeff. 



Genus 4. BoneUia, Rolando. 



5. BoneUia suhmii, n. sp. 



B. Gephyrea ach^ta. 



Genus 5. Phascolosoma, F. S. Leuckart (s. str. Selenka and de Man), 

 (a) Proboscis with four retractors. Hooks present. 



6. Phascolosoma vtdgare, de Blainville. 



7. Phascolosoma vidgare, var. astiita, nov. 



8. Phascolosoma pudicum, u. sp. 



1 We have an exception in tlie Plujmosoma granulatum of tlie Meiliterranean, wliicli is most closely allied to the 

 Phymosoma scolops of the Red Sea and Pacific and Indian Oceans, and which has doubtless found its way from the Red 

 Sea into the Mediterranean. 



2 Die Ripunculiden, eine systematische Monographic, nnter Mitwirkung von Dr. J. G. de Man and Dr. C. Biilow 

 hearbeitet vnn Dr. Erail Selenka; in Semper's Reisen im Archipel der Philippinen, Theil. II. Bd. iv. Abth. 1, also 

 separately, Wiesbaden, 1883. 



