YEKMES AXD MOLLUSCA OF THE DEEP SEA 117 



in shells such as Phascolion and Pkascolosoma, that 

 are more frequently found at the greater depths ; but, 

 apart from this, there are no characters that exclu- 

 sively belong to the abysmal Gephyrea or are more 

 frequently found in them than in the shallow-water 

 forms. Nor are there any genera, at present brought 

 to light, that are confined to those regions of the sea. 



The group of the Annelida is not very well 

 represented in the deep-sea fauna. The genera 

 Serpula and Terebella have been found very widely 

 distributed over the earth, at all depths from the shore 

 to the abyss, but there do not seem to be many genera 

 that are confined to deep. water. In some cases, where 

 there is a scarcity of lime in the water, the thin pro- 

 tecting tubes of the sedentary forms are strengthened 

 by the adhesion of foreign particles, such as sponge 

 spicules and arenaceous foramiiiifera. but in others, 

 the tubes are formed of successive layers of a trans- 

 parent quill-like substance (Xothria Willemoesii) 

 which is frequently armed with spiny projections. 



Most of the errant Polychastes found at great 

 depths are said to be most brilliantly coloured, and 

 some of these, such as Eunice amphiheliie, have the 

 power of emitting a bright phosphorescent light ; but 

 there seem to be no very definite and constant 



