30 jiNNALS NEW YORK ACADEMY OF SCIENCES 



opment of varices. It differs also in color, being nearly white. The few- 

 pale brown spots are visible only with a lens. 



h. American Species 

 Cerithium eburneum Bruguicre 



1792. Cerithium eburneum Bruguicre, Hist. Nat. des Vers, Encyclop. Method., 

 I, pt. 2, 438. 



1887. Cerithium eburneum Tryon, Manual of Conch.. IX, 129, pi. 22, fig. 75. 



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

 nitz. Bd. I, Abth. 26, 219, pi. .39. figs. 3-0. 



Measurements: Length, 25.7 mm.; greatest diameter, 11 mm.; apical angle, 

 34°, changing to 29.5° on the ninth volution ; sutural angle. 85.5°. 



Color: White, irregularly marked with patches of color which vary from 

 golden brown to dark reddish brown. 



The youngest volution preserved, which is probably the first beyond the 

 protoeonch, is .5 mm. in diameter. It has two equal spirals, which re- 

 main the only ornamentation of the shell for about one-fourth of a volu- 

 tion. Less accelerated individuals retain this ornamentation for a com- 

 plete volution. The next features to appear are ribs and two fine spirals 

 on the shoulder. Intercalated spirals are first introduced on the fourth 

 of the volutions preserved, and the same type of ornamentation continues, 

 with the addition of fine spirals for eight volutions. Beyond this the 

 ribs become ill defined and gradually break up into rows of nodes, which 

 are developed on all the strong spirals until, on the volution before the 

 last, there are five such rows. At about the ninth volution the lower of 

 the two primary spirals becomes weaker, while the upper remains strong 

 and defines a slight shoulder at about the middle of the volution. Varices 

 are irregularly developed with not more than two on a volution, and fre- 

 quently less than two. 



The aperture is oval, and a posterior tooth is well developed. The 

 anterior canal is short and rather widely open. The outer lip is crenu- 

 lated, and the callus of the inner lip is thick and narrow. 



Horizon and localities : Recent. West Indies, Florida. 

 No. 201.35, Columbia University collection. 



Eemarks : The development of this species and its general form are so 

 closely similar to those of Ceritliium tiibcrosum, as to leave little doubt of 

 their descent from a common ancestor, in spite of the fact that the two 

 shells come from such widely separated localities as the West Indies and 

 the Eed Sea. The American species of other genera, as well as Cerithium, 



