176 SBDENTARIA. 



tal plane, depressed and adhering below. The aperture teP 

 minal and rounded or angular. 



Spirorbis nautiluiJes The Nautilus-shaped Spir- 



oRBis. Plate XIX. fig. 15. White, nautilus-shaped, trans- 

 versely wrinkled. One-eighth of an inch in diameter. In- 

 habits the British coasts, on Algae, &c. 



TRIBE II. AMPHITRIT^A. 



Branchiae not separate or covered by an operculum, and 

 disposed anteriorly ; tube membranous, or horny, and more 

 or less arenaceous. 



* With large branchiae on tentacula. 

 Genus 6.- AMFRITRITE.— Lamarck. 



Generic Character. — Body tubicolar, elongated, cylin- 

 drical, attenuated behind, with many annulated segments ; a 

 single row of setiferous papillae ; subulate, fasciculate bristles 

 and hooked setae ; branchiae in slender finger-shaped fasciculi, 

 disposed like a fan, and spreading into a disk ; two short 

 subulate filaments inserted at the internal base of the 

 branchiae, between which is a terminal mouth ; tube elon- 

 gated, cylindrical, tapering towards the base, membranous or 

 coriaceous, and generally naked. 



Amphitrite ventilabrum The Fan Amphitrite. Plate 



XIX. fig. 19. Tube tapering, incurved, and smooth; of a 

 cream yellow colour. Inhabits the Mediterranean sea. 



Genus 7.— TEREBELLA Lamarck. 



Generic Character. — Body tubicolar, elongated, cylindri- 

 cal, attenuated posteriorly, segments transverse, and sub- 

 annulated ; having a row of nodulous and setiferous papillas 

 on each side ; with numerous filiform, twisted tentacula sur- 

 rounding the mouth, and terminating in front of it; two rows 

 of ramose branchiae placed in a single row beneath the ten- 



