Cerithiidae 141 



to 14, flat whorls regularly increasing in size; sutures distinct, ex- 

 cavated; sculpture of three equal-sized spiral ridges, flattened on 

 top; concave interspaces with fine spiral striations above ridges and 

 delicate axial striations which do not cross ridges. Body whorl has 

 four spirals, one smaller ridge at circumference of base. Aperture 

 oval; outer lip crenulated with external sculpture; anterior canal 

 central, short, open, recurved; operculum corneous. 



Common in shallow water. Often found about oyster bars, within 

 large dead shells. 



Family CERITHIIDAE 



The Cerithiidae are mollusks of tropical and semitropical seas. 

 Many of the species are littoral, living among sea grasses and weeds; 

 others frequent rocky bottoms in deeper water. 



The animals are vegetarian and the sexes are separate. A pedal 

 gland secretes threads of mucus by means of which the mollusks 

 can attach themselves to any convenient object, or hang suspended 

 beneath the surface film of water. 



Shells of the Cerithiidae vary in form within certain limits; all 

 are elongate, many whorled, with a small oblique aperture and a 

 short anterior canal. 



Genus CERITHIUM Bruguiere, 1789 

 Cerithiom alg-icola^ss c. B. Adams PI. 27, fig. 193 



Alt., 20-27 mm. Shell white with brown markings usually dis- 

 posed in more or less revolving pattern. Spire elongate, tapering to 

 acute apex; eight to ten convex whorls, angulated by axial ribs; 

 sutures narrow, incised. Sculpture of eight or ten indefinite longi- 

 tudinal ribs or varices, interrupted at sutures and angulated at peri- 

 phery of whorls; a nodular spiral line immediately below suture 

 on body and penultimate whorls; three headed spirals below peri- 

 phery of body whorl, fine spiral threads between the stronger sculp- 

 ture; a thickened varix opposite aperture; aperture oval, oblique, 

 outer lip thin, crenulate; anterior canal short, oblique; columella 

 with transverse fold above, which defines a short posterior channel; 



-^2 Gr., keration, little horn — N. L., alglcola, living on seaweed. 



