50 EXPLANATION OF PLATES. 



resented as expanded with the oral disk turned towards the 

 observer. 



Fig. 6. The same partially contracted with oral disk turned 

 from the observer (life-size). 



Plate vii. 



Fig. 1. A rocky mass formed of the worm tubes of Sabella 

 Pacifica cemented together. The section of this mass with the 

 ramifying tubes appears in the foreground : the external tube 

 openings on the smooth, upper side. The intervals between the 

 tubes is filled up by a clay-like material semi-solidified. A pit 

 is seen in the middle of the figure, from which protrude the 

 edges of the shells of several small mussels which were alive 

 when the mass was drawn and which have become embedded in 

 the growing mass, hermetically imprisoned in this pit. 



Fig. 2. Sabella Pacifica removed from the mass figured 

 above. 



Fig. 3. Portion of a large cluster of sand tubes of Sabel- 

 laria Californica sp. nov. This was cut from a mass four feet 

 long and of about the same width and eighteen inches thick. 

 The upper part shows the external openings, the lower fore- 

 ground sections of the tubes. On either side the tubes are 

 shown. The rounded bodies or disks shown closing several of 

 the external orifices of the tubes are opercula of the inhabitant 

 of the tube. 



Fig. 4. Sabellaria CaZt/brnica extracted from its tube. The 

 dorsal region is on the lower side of the figure. The body is 

 verj' much contracted, and the posterior end of the body is 

 bent downward. Its position, when alive, is probably bent to 

 the other side of the anterior end, the posterior opening being 

 thus brought near the operculum. 



