SERPULIDAE. 473 



In this family the tube is formed of mucin impregnated with calcareous 

 matter and is usually open at but one end, which is typically closed by the 

 operculum. These tubes are ordinarily fixed to sohd objects, such as rocks and 

 shells. They take the most varied configurations, occasionally straight to sig- 

 moidally curved or irregularly sinuous and loosely coiled, and the forms in which 

 coiled into a nautiloid spire either over the entire length or only over the posterior 

 portion. While the inner surface, or bore, is smooth and uniform, the outer 

 surface may be very uneven from supporting processes in the form of spines or 

 keels. The tubes are often single but they may be aggregated into polypiform 

 groups, as is normal in the genera Filograna and Salmacina and as occurs in 

 Serpula vermicularis Linne and Pomotoceros triqueter Linne. Some forms 

 have their tubes entirely free. As with the sabellids, there is some evidence 

 that the serpulids may occasionally leave their tubes entirely. 



Both sabellids and serpulids occur for the most part in water of small 

 depths; but exceptionally a species is taken in very deep water, such being 

 Placostegus benthalianus Mcintosh, which was dredged by the Challenger 

 at 3,125 fms. 



Some species are hermaphroditic; and Salmacina dysteri Huxley is not 

 only hermaphroditic but also viviparous (Edinb. new philos. journ., 1855, new 

 ser., 1, p. 113, fig. 1-11). It has also more recently been demonstrated that 

 a sexual multiplication by budding and fission occurs in the group (Malaquin, 

 Compt. rendus Acad, sci., 1905). 



Key to Genera. 



a. Uncini with teeth exceedingly fine and numerous, the series terminated at the cephahc end by a 

 proportionately long, entire spine; plate emarginate deeply at the posterior end beneath. 

 b. No operculum; thoracic setae all of the ordinary limbate type, 

 c. Branchial lobes not spiral. 



d. No thoracic membrane Salmacinopsis Bush. 



dd. A thoracic membrane present. 



e. Collar three-lobed; branchiae in a semicircle Subprotula Bush. 



ee. Collar entire; branchiae in a circle Psygnwhranchus Philippi. 



cc. Branchial lobes spiral. 



d. Abdominal setae falcate Protula Hisso. 



dd. Abdominal setae obliquely bayonet-formed, border plaited Frolulopsis St. Josepli. 



bb. With a globular or ampuUiform operculum; thoracic setae not all of the ordinary limbate type, 

 c. Setae of fkst thoracic somite like those of the succeeding thoracic somites, partly simply limbate 

 and partly terminating in a falcate blade, below which is a short limbus. 



d. Abdominal setae^falcate Apotnatus Morch. 



dd. Abdominal setae geniculate Apomatopsin St. Joseph. 



cc. Setae^offfirst somite in part simple and non-limbate and in part having a crenulate Umbus or 

 wing;^ setae of all other thoracic somites non-limbate, curved, with denticulations on the 



convex side Cystopomatus Gravier. 



a a. Uncini not of this form. 



