472 THE ANNELIDA POLYCHAETA. 



Dasychonopsis Bush. 



Harriman, Alaska Exped., 1910, 12, p. 191, 198. 

 Dasychone Avct. (ex part.). 



Dasychonopsis nigromaculata (Baird). 



Sabella nigromaculata Baird, Journ. Linn. soc. London, 1865, 8, p. 159, pi. 5, fig. 5, 6. 

 Dasychone nigromaculata McIntosii, Challenger annelids, 1885, p. 503, pi. 53, fig. 5, pi. 31A, fig. 4-6; 

 pi. 39A, fig. 6. 



A single specimen taken on Abrolhos Island, off Brazil, 28 December, 1887. 

 It is about 44 mm. long, inclusive of branchiae, and 34mm. without; width 

 across abdomen, 6.5 mm. There are but thirty-seven branchiae on each side 

 in place of forty-two or forty-three given by Mcintosh for his specimen from 

 St. Thomas. The setae and uncini agree essentially in form. The species is 

 also known from St. Vincent. 



Serpulidae. 



In their general structural characteristics these polychaetes are very similar 

 to the Sabellidae, with which they are by some united into a single family. 

 They never attain the size of the larger sabellids, rarely exceeding ten or twelve 

 centimeters in length. While their coloration is not so conspicuously displayed 

 as among the sabelUds, it is often varied and attractive, varying much even 

 with the same species. 



In contrast with the preceding family an operculum is in most cases present, 

 this being formed by the dilatation of one or more of the branchial filaments, 

 which may be altered as a whole or which may retain the normal structure 

 below the operculum proper. The operculum may be simply membranous, 

 may be of horny consistence, or may possess a calcareous plate. Plates and 

 processes of a great variety of form may be developed on the operculum. The 

 position and number of opercula are subject to considerable variation in certain 

 species. 



A thoracic membrane, representing the fused cirri, is nearly always present. 



The general arrangement of the parapodia and the forms of setae and 

 uncini is, in general, as in the preceding family. 



Ventral glands confined to the thorax. 



There is no definite ciliated groove, though the ventral surface, and some- 

 times the dorsal, may be in part ciliated. 



