CRETACEOUS FOSSILS. 263 



CERITHIUM, Brug. 



C. Mexicanum, n. s. 



PL 35, Pig. 8. 



Shell elongate, slender; whorls numerous, rounded on the 

 sides ; suture linear, impressed. Surface marked by numerous, 

 slightly curved longitudinal ribs, about twenty-five to a volution ; 

 these are crossed by five or six revolving ribs, which produce a 

 small node at each crossing of the longitudinal ribs; between 

 each pair are two or three minute revolving lines. On each 

 volution there is one longitudinal rib, larger than the others, 

 which seems to be a regular varix; these are irregularly placed, 

 but on six whorls there are but six of these varices. They are 

 not constant in size, and on the upper whorls, where the longi- 

 tudinal ribs are less numerous, and proportionally larger, they 

 assimilate them more nearly in appearance. Aperture broad, 

 inner margin somewhat thickened and flattened. 



Length of fragment, less anterior portion of aperture and several apical whorls, 

 1.1 inch. 

 Pare. But two or three specimens were found. 



TURRITELLA, Lam. 



T. SERIATIM-GRANTJLATA, Roem. 



Under this head, among the Californian fossils, I have already given the 

 synonymy of this species: see the enumeration [ante). The shell is very common, 

 and is extremely variable in the details of its ornament, both in the number and 

 in the arrangement of its ribs. Its apical angle is also somewhat variable. 



