GASTEEOPODA. 



[Family YEHMETiDiE.] 



The shells of species of this family are distinguished from 

 those of the Serpulce by the presence of a spiral nucleus and of 

 concave smooth interior septa. 



If the shell is formed of a solid matter strongly sculptured 

 with longitudinal grooves or scales, or of a brownish colour, it 

 is certainly formed by a Vermetus; but if the shell is of a soft 

 earthy matter, feebly longitudinally grooved, it is doubtful to 

 which it belongs. 



The shells of the SerpuUdce have an anal opening (except 

 Cymosinra), and appear only to be composed of two layers, the 

 Vermetidce having three. 



The interior of several species contains very long lamellae, 

 generally regarded of generic value ; but they are dissolved 

 with age, like the teeth of some species of Fupa. 



All the Vermeti are viviparous, and the lamellae within the 

 tubes may serve for the retention of the fry. 



The genera and sub-genera contained in this family are Yer- 

 METUS [Petaloconchus, Serpulorbis) (p. 249), and Siliquajria 

 (p. 249). 



[Family C^cid^.] 



81iell with a spiral nucleus; tubular, regular, sometimes 

 fixed aperture orbicular ; operculum horny, multispiral ; margin 

 sometimes fimbriated. 



CiECUM, Fleming.* 



Nuclear ivhorls orbicular, in the same plane as the adult, fre- 

 quently decollated ; operculum concave or flattened. 



Sections : — Elejpliantulum. Comparatively of large size, tapering; 

 sculpture longitudinal. 

 Distribution, 9 species. Mazatlan (6), "West Indies, Mauritius. 

 Fossil, 1 species (0. liratum). Carpenter. Cor. Crag. Sutton. 



Anellum (typical Caeca). Adult shell annulated. 

 JDistrihution, 14 species. Europe, Matzatlan, Australia, Japan. 

 Fossil, 2 species. Eocene. Paris, Sufi'olk. 



Fartulum. Smooth, cylindrical. 



Distribution, 10 species. Mazatlan, Tenerifie, Singapore, 

 Australia. 



Fossil, C. mamillatum, S. Wood. Cor. Crag. Sutton. 



Sub-genera : — Beochin'A, Gray. 

 Tyjpe, Dentalium glabrum, Mont. 



* See p. 2d9, 



C 25 



