484 THE ANNELIDA POLYCHAETA. 



ing somite, is ordinarily detectable (Caullery, Bull. Soc. zool. France, 1913, 

 38, p. 198). 



There is a distinct thoracic region embracing, in addition to the highly 

 modified first setigerous somite, a second somite, in which only the neuropodium 

 is represented similarly by a small fascicle of capillary setae, this being followed 

 by three or four somites in which both neuropodia and notopodia are strongly 

 developed. These are sometimes spoken of as the parathoracic somites. The 

 notopodia of these somites are strongly developed, each consisting of a lamina 

 more or less elongate vertically and bearing stout paleae and usually, in addition, 

 some finer setae, the paleae and setae directed more or less obliquely caudad. 

 The neuropodia are smaller, but bear corresponding, though finer, more weakly 

 developed setae. In the abdominal region the notopodia are in the form of 

 greatly elongate tori bearing uncini, while the smaller neuropodia bear each a 

 fascicle of barbulate capillary setae. Dorsal cirri are present over most of the 

 length of the body and appear to function more or less as branchiae. 



The sabellariids for the most part construct tubes of sand which in some 

 cases may be united in great numbers and form masses several feet thick. 

 Sometimes the tubes of different species are united, as, for example, those of 

 Sabellaria alveolata with those of S. spinulosa (St. Joseph, Ann. sci. nat., 1894, 

 ser. 5, 17, p. 159). They are essentially shallow water forms. 



Key to Genera. 



a. With no operculum Cryptopomatus Gravier. 



aa. With a well-developed operculum. 



b. Opercular lobes separated, each one bearing a single, someAvhat spiral series of long paleae. 



Phalacrostemma Marenzeller. 

 bh. Opercular lobes more or less fused dorsally, with paleae shorter and in two or three series. 

 c. Paleae in two series. 

 d. With dorsal hooks. 



e. With three parathoracic somites Idanthyrsus Kinberg. 



ee. With four parathoracic somites Tetreres Caullery. 



dd. With no dorsal hooks Centrocorone Grube. 



cc. Paleae in three series Sabellaria Lamarck. 



Synonymy of Genera. 



Hermella Savigny (1820), Phragmatopoma Morch, Psammatolus Guettard, 

 and Chrysodon Oken, are synonyms of Sabellaria Lamarck. 



Ariapithes and Lygdamis Kinberg (18GG) are not suflSciently known to 

 be placed with certainty. 



i 



