SEDENTARIA. 175 



uated towards the posterior part, and provided towards the 

 upper part with a simple, testaceous, orbicular operculum ; 

 tube testaceous, cylindrical, posteriorly narrowed, more or 

 less twisted, and adhering by the side to marine substances; 

 aperture round, and the margin frequently provided with 

 from one to three denticles. 

 Shells attached by oue side to marine bodies. 



Vermilia triquetra The Triangular Vermilia. Plate 



XIX. fig. 18. White or reddish, rugged, variously twisted, 

 and triangular ; carinated along the back. Inhabits the coasts 

 of Britain. 



Genus 4 SERPULA — Lamarck. 



Generic Character. — Body tubicolar, elongated, depressed, 

 and attenuated behind ; segments numerous, and narrow ; 

 small bundles of awl-shaped bristles, in a single row on each 

 side, and also hooked bristles ; branchiae terminal, fan-shaped, 

 and deeply cleft into pinnated, or plumose finger-like divi- 

 sions ; mouth terminal, placed between the branchiae, and 

 surmounted by a pedicled infundi buliform, or club-shaped 

 operculum ; tube solid, testaceous, irregularly twisted, 

 either grouped or solitary, fixed, with a rounded and terminal 

 aperture. 

 Found solitary, or in groups curiously intertwined. 



Serpula vermlcularis. — The Vermicular Serpdla. 

 Plate XIX. fig. 14. White, cylindrical, tapering, rugged, 

 variously curved and twisted. Inhabits the coasts of 

 Britain. 



Genus 5.— SPIRORBIS Lamarck. 



Generic Character. — Body tubular, subcylindrical, pos- 

 teriorly attenuated ; six pinnated retractile branchiae, in 

 radiated expansions, at the anterior extremity ; operculum 

 placed between the branchiae, pedicellate, peltate ; tube tes- 

 taceous, spirally twisted into an orbicular form or a horizon- 



