THE COAST OF CALIFORNIA. 131 



tracted, for the aggregation is exposed for several hours 

 between tides. 



The body of the Sabellaria which forms these tubes is 

 composed of two regions, a spiniferous anterior, and a 

 non-spiniferous posterior body region. The anterior is 

 segmented ; the posterior unsegmented. Both are capable 

 of great extension ; the former being much thicker than 

 the latter, which resembles somewhat an appendage to the 

 former. 



The operculum is round, low conical, with black radial 

 ridges. On its edges there is a marked coloration. It is 

 mounted on a contracted base and when the worm is re- 

 tracted the operculum effectually closes the openings of 

 the worm cases. 



On each side of the operculum there is a tuft of fila- 

 ments which are the branchiae. They are simple, un- 

 branched, flexible, extensile appendages and have a pur- 

 ple color at their bases. They lie on the oral and lateral 

 regions of the head. 



The mouth bears on each side a bifid structure of some- 

 what crescentic shape, and is enclosed by three lips, an 

 anterior and two lateral posterior. 



The first body segment lies just below or behind the 

 oral aperture, and bears a bundle of serrated spines. The 

 second, third and fourth body segments are somewhat dif- 

 ferent from those which follow. They bear on each side 

 a comb-like structure, on the ventral side of which there is 

 a small prominence with serrated setse, and on the dorsal 

 a filamentous branchia. The first body segments bear the 

 two clusters or clumps of spines of the mouth, and the two 

 small filamentous appendages. 



The fifth and following body segments support on either 

 side a fin-like protuberance of rectangular shape, without 

 comb-shaped structures. This fold has on its outer edge 

 ESSEX INST. BULLETIN, VOL. xxi 9* 



