356 VERMETIDiE. 



As may be inferred from the synonymy, this curious 

 little genus has puzzled many Zoologists ; among other 

 genera it has been referred to the Pteropodous Styliola, 

 and to the extinct, Cephalopodous Orthoceras ; there are 

 two British species, living in about ten fathoms water. 



Species of C cecum. 



diminutiim, C. B. Adams. monstrosum, C. B. Adams. 



eburneum, C. B. Adam.s. parvum, C. B. Adams. 



firmatum, C. B. Adams. pulchellum, Stimp. 



glabrum, Mont. pygmseum, C. B. Adams. 



laeve, C. B. Adams. trachea, Mont. 

 laqueatum, C. B. Adams. 



Fam. VERMETIDiE. 



Lingual dentition — ? Rostrum produced; tentacles 

 short, triangular, eyes small, at their external bases. 

 Mantle with the margin entire, embracing the neck ; gills 

 enclosed in a line on the left side of the mantle-cavity. 

 Foot cylindrical, not serving for locomotion, dilated, sub- 

 clavate, or truncated in front. 



Operculum horny, circular, many-whorled, or wanting. 



Shell irregularly twisted, tubular, attached, often regu- 

 larly spiral when young ; aperture round. 



The Operculum is very large in Vermetus, wanting in 

 Serpulorbis, very small in Bivonia, and singularly deve- 

 loped in Tenagoda. 



Genus SIPHONIUM, Browne. 



Operculum large, smooth, circular, concave j scar cen- 

 tral, circular, rugose. 



