338 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



or anteriorly, the inner ones toward the center.) Nuchal hooks are absent. 

 The thorax includes 2 anterior thoracic segments provided with only 

 capillary setae, and 3 parathoracic segments provided with flattened 

 paleae dorsally, and similar, though much smaller, setae ventrally. The 

 abdomen consists of a variable number of segments; its notopodia are 

 provided with tori bearing uncini and its neuropodia with fascicles of 

 fine setae. The caudal tail (=cauda) is smooth, cylindrical, sharply set 

 oE from the abdomen. Oral tentacles are present, arranged in 7 to 1 1 

 ranks of transverse rows. The paired palpi are simple, taper distally, and 

 are usually more or less concealed from view by the oral tentacles. 



Species of the genus Sabellaria appear much alike in minute details 

 save in characters of the operculum. The major differences are believed 

 to be in the terminal portions of the opercular paleae, especially in those 

 of the middle and inner series. The outer paleae are often distally serru- 

 late, the middle portion more or less prolonged, sometimes as a spike, 

 with or without surface ornamentation, or it may be more or less finely 

 serrated. When uninjured, this character is usually highly diagnostic. 

 Those of the middle row are even more specific ; they may be of a single 

 kind (pi. 32, fig. 51) or they may alternate long and short (pi. 31, figs. 

 37, 38). The paleae of the inner row are usually directed inward, toward 

 the center of the disk; usually they terminate in a point (pi. 30, fig. 42), 

 but in a few species they are distally serrated (pi. 31, fig. 40). This may 

 be summarized as follows, for the species herein considered. 

 Inner paleae distally serrated. 



Middle paleae all of the same length : S. belliSj S. moorei. 



Middle paleae alternate long and short : S. floridensis. 

 Inner paleae distally entire. 



Middle paleae all of the same length. 



Outer paleae with bifurcated tip : S. fissidens. 



Outer paleae with simple spike : S. nanella. 



Outer paleae with penicillate spike: S. cementarium, S. 



vulgaris, and subsp. beaufortensis. 

 Outer paleae with serrated tip : S. spinulosa, S. gracilis. 



Middle paleae alternate long and short : S. bella, S. alcocki. 

 Other features concerning the thoracic and abdominal setae and hooks 

 are usually too uniform from one species to the next for specific distinc- 

 tion. Most, perhaps all, species of Sabellaria are colonial, construct tubes 

 of cemented sand that adhere to one another; they sometimes make up 

 masses of great extent. The size of sand particle used may have some 

 significance. 



