WOOD, PHYLOGENY OF CERTAIN CERITHIIDJE 29 



well defined, and the neanic whorls lack altogether the strongly spinose 

 character of C. echinatum at the same age. The apical angle of C. album 

 is much wider, and the abrupt change in the slope of the sides on the last 

 two volutions is not found on C. echinatum. The youngest stages of this 

 shell are closely similar to those of the species already described, but in 

 the adult the ornamentation develops rows of small nodes instead of the- 

 shoulder angle present on many species of the group. 



Cerithium graciliforme Sozverby 



186G. Cerithium graciliforme Soweeby, apud Reeve, Conch. Iconica, XV, No. 49. 

 1887. Cerithium ebumeum Tryon. Manual of Conch., IX. 129, pi. 22, fig. 77. 

 1898. Cerithium graciliforme Kobelt, Syst. Conch.-Cabinet von Martini u, 

 Chemnitz, Bd. I, Abth. 26, 124, pi. 24, fig. 9. 



Measurements : Length, 24.2 mm. ; greatest diameter, 9.7 mm. ; apical angle, 

 35.3°, changing on the ninth volution to 26° ; sutviral angle, 86.7°. 

 Color : White with occasional spots of pale brown. 



The youngest volution preserved is .5 mm. in diameter, but it is toa 

 much corroded to show its form. The next volution is also much worn, 

 but shows that it has two equal spirals crossed by ribs. On the third 

 volution the same type of ornamentation continues, with three fine spirals 

 on the shoulder. A single spiral is intercalated between the two primary 

 ones on the fourth volution, and there are four fine spirals on the shoulder 

 and one on the lower slope of the whorl. On the fifth volution, three 

 varices are developed, while the ribs between them become much narrower. 

 Varices continue to be formed throughout the life of the shell and con- 

 stitute a striking feature of its ornament. The shoulder becomes nearly 

 obsolete, and the ribs break up into nodes until, on the tenth volution, 

 the surface is marked by a strong varix and four rows of nodes, of which 

 the second below the suture is weaker than the others. This type of orna- 

 mentation continues for the remaining three volutions. 



The aperture is broadly oval. A posterior tooth is present, but is not 

 strongly developed. The callus of the inner lip is thin, and the outer lip 

 is nearly smooth. The canal is short and slightly reflexed at the margin. 



Horizon and locality: Recent. The locality of this species is not given ia 

 any of the descriptions of it tliat have been published, and the specimen in 

 the Columbia University collection is also unlabeled. 



No. 20134, Columbia University collection. 



Remarks : This species resembles most closely Cerithium eburneum, 

 and is considered only a variety of that species by Tryon; but it differs 

 in its more slender form, nearly obsolete shoulder and in the great devel- 



