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 one 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 vermicularis. — 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- 



