CERITHIID^. 113 



Central tooth of the rachda nmlticuspidate, lateral securiform, 

 the margin toothed, marginals narrow, with coml)dike extremities 

 (PI. 19, fig. 1). 



Marine, inhabiting temperate and tropical seas ; fossil, nearly 500 

 species are enumerated, commencing in the Trias and attaining it? 

 maximum development in the Cretaceous. 



Subgenus Cerithium (sensu stricto). 



Columella thickened, with a tooth-like posterior tubercle, outer 

 lip dilated at the base, whorls varicose. 



Section Colin A, H. and A. Adams, 1853. 



Shell elongated, whorls numerous, convex, nodulous, spirally 

 striated , aperture oval, prolonged in front into a short recurved 

 canal, columella simple, oblique, outer lip expanded and reflexed. 

 Middle whorls gibbous, sculpture usually obsolete on the last whorl. 



The few sjiecies inhabit deep water, sandy bottom, at the Philip- 

 pines, China, etc. 



Section Liocerithium, Tryon, 1887. 



Shell pupoidal or subcylindrical, without ribs or nodules, usually 

 spirally grooved. C. incisum, Sowb. 



Subgenus Stilus, Jeffreys, 1885. 



Shell spit-shaped, reticulated ; apex forming a twisted and 

 abruptly semi-detached peak ; l)asal groove short and recurved. S. 

 iNSiGXis, Jeffreys. 



Subgenus Cerithioderma, Conrad, 1860. 



Acutely ovate, striate ; lip grooved, umbilicated, columella 

 recurved inferiorly or subtruncate ; aperture patulous, margin 

 obtusely rounded inferiorly ; beak very short, narrow, recurved. 



Fossil only. C. prima, Conr. Eocene, Alabama (Struct, and 

 Syst. Conch., t. 69, f 51). 



? Subgenus Brachytreinia, Morris and Lycett, 1850. 



Shell turreted, turbinate, solid, whorls nodose, costulate or can- 

 cellate, the last whorl large, ventricose, angulated ; columella 

 smooth, rounded, obliquely truncate at the base forming a short 

 oblique canal, aperture obsoleteh' channeled above, lip thickened 

 and usually exteriorly subvaricose. C. Wrighti, Cotteau (PI. 19, 

 fig. 8), 16 sp., Jurassic, Europe. 



