48 ANNALS NEW YORK ACADEMY OF SCIENCES 



developed from suture to suture. The first, fourth and eighth ribs are 

 much stronger than the others, forming varices. On the later vohitions, 

 these varices appear at irregular and less frequent intervals, having in 

 the adult from five to ten ribs between the varices. On the succeeding 

 volutions more spirals appear, until those of the fifth order may be 

 counted. These are ver}^ fine, but still preserve their rounded character, 

 and several of equal strength are crowded between the coarser spirals. 

 The strong shoulder and the two equal primary spirals persist until the 

 body volution is reached. On the latter volution the primary spiral on 

 the shoulder becomes as strong as the primary ones below it, and the 

 shoulder, which is still present on the preceding volution, disappears. The 

 body volution bears below the three primary spirals already mentioned 

 three more strong spirals, with finer ones between them. Here, too, the 

 ribs become weaker, the spirals stronger, and at the crossing of the two 

 there is a tendency to form nodes, though the development does not go 

 far enough to form actual nodes. On the later portion of the body whorl 

 the sub-sutural spiral becomes as strong as the two primary ones. 



The aperture of the shell is oval, with short, reflexed anterior canal. A 

 well-defined posterior canal is also present, the inner margin of which is 

 bounded by a ridge, but not a distinct tooth, such as appears in Cerithiuni 

 fiihrrosiim. The inner lip is covered by a narrow callus, and the outer 

 lip is slightly flaring and notched to correspond v/ith the strong spirals 

 of the exterior surface. 



Horizon and i>ocaijty : Tbe precise horizon of this species is not known, but 

 it was found in a collection of unidentified shells from the Eocenic of the 

 Paris Basin. 



No. 10323, Columbia University collection. 



Remarks : CerWiium cequispirale has a close resemblance in form and 

 in the features of the aperture to C. lamellosum, but it differs from that 

 species in the character of the spirals, which are strongly developed and 

 have a rounded form instead of appearing like imbricating lamellfe, as in 

 the latter species. C. lamellosum also differs in the loss of its secondary 

 spirals on the adult whorls. 



C. cequispirale has the two strong spirals and the numerous spirals of 

 higher order characteristic of C. tuberosum, and it retains these features 

 throughout life. The body volution has especially strong spirals on its 

 lower slope, and the lower part of the outer lip grows a little more rapidly 

 than the upper part. The persistence and development of this tendency 

 would in time produce a strong projection of the lower spirals like that 

 seen on the aperture of C. tuberosum. At the same time the prominent 



