irOOD, PHYLOGENY OF CERTAIN CERITHIWM 33 



Cerithium citrinum Sozi:crby 



1855. Cerithium citrinum Sowekby, Thesaurus Conch., II, 855, pi. 179, fig. 66. 

 186(3. Cerithium citrinum Reeve, Conch. Icon., No. 1, pi. 1, fig. 1. 

 1887. Cerithium citrinum Tkyon, Manual of Conch., IX, 123, pi. 20, fig. 21. 

 1898. Cerithium citrinum Kobelt, Syst. Conch.-Cabiuet von Martini u. Chem- 

 nitz, Bd. I, Abth. 26, 110, pi. 22, fig. 23. 



Measurements: Length, 30.5 torn.; greatest diameter, 15.5 mm.; apical 

 angle, 37° ; sutural angle, 87°. 



Color: Cream white, with streaks and patches of pale brown. 



The youngest vohition preserved on this shell is 3 mm. in diameter, 

 and its ornamentation is similar to that of the fourth volution on C. 

 menkei. It has two strong equal spirals, one intercalated spiral and 

 five fine spirals on the shoulder. One spiral is on the lower slope of the 

 whorl. The ribs on this species are broad and, for the first five volu- 

 tions, broader than the spaces between them. The two primary spirals 

 remain equal in strength for seven volutions, after which the lower spiral 

 is weaker, but the outline of the volution never becomes sharply angular, 

 as in the preceding species. The secondary spirals of the shoulder and 

 the lower slope of the whorl become as strong as the primary ones, and 

 the outline of the volution becomes regularly curved. Extremely fine 

 spirals of higher order are rapidly introduced, while the primary and 

 secondary spirals are raised into ridges carrying the finer spirals with 

 them, so that the whole surface appears to be covered with bundles of 

 fine spirals having deep grooves between them. The ribs disappear on 

 the body volution, with the exception of one strong varix on the side op- 

 posite the aperture, as is usual in shells of this group. Nodes are absent 

 from the entire surface. 



The aperture is broadly oval. The callus of the inner lip is thick and 

 narrow, with a prominent posterior tooth. The anterior canal is long 

 and the margin of the outer lip thick and crenulated. 



Horizon and locality : Recent. Bird Islands, Pacific Ocean. 

 No. 20128, Columbia University collection. 



Eemarks: Cerithium citrinum differs from C. columna in the more 

 delicate surface ornamentation, the rounded outline of the volutions and, 

 with the exception of one varix, the absence of ribs and nodes on the 

 body volution. It also has a longer anterior canal. This species differs 

 from C menTcei in the absence of sharply angular volutions and in the 

 disappearance of ribs on the body whorl. 



