SEA-WORMS. 113 



with its ridge-shaped tube, which earns its scientific name 

 (Serpula triquetrd). Of the three flat surfaces implied in 

 that name one is cemented throughout its length to the shell 

 or stone it has selected for its freehold. A third species (S. 

 vermicularis) secretes a round tube, but may be readily dis- 



SCARLET SERPULA. 



tinguished from S. contoriuplicata, by its possession of a 

 double stopper with toothed edges. 



One of the most plentiful of these tube-making worms is the 

 Spirorbis, which is to be found everywhere on stones, rocks, 

 and weeds in the littoral zone. More especially shall we be 



