WOOD, PHYLOGENY OF CERTAIN CERITHIID^ 21 



Cerithium menkei Deshayes 

 Plate VII, figs, 2, 3; plate viii, fig. 3; plate ix, fig. 2. 



18G3. Ccrlthuuu iiiciikei Deshayes, Moll. Reunion, p. 97, pi. 9, fig. 15. 

 1887. CcrithUtm coltinnia Tryon, Manual of Couch., IX, 123, pi. 20, fig. 19. 

 1898. CeriihUtm menisci Kobelt, Syst. Conch.-Cabiuet von Martini u. Chem- 

 nitz. Bd. I. Abth. 26, 208, pi. 37, fig. 1. 



Measukements : Length, 29 mm. ; greatest diameter, 16.5 mm. ; apical angle 

 to the eighth volution, 47°, changing to 35° ; sutural angle, 76.5°. 



Color : Uniformly cream-colored, or occasionally having a few pale brownish 

 spots scattered irregularly over the surface. 



This shell is thin and delicately sculptured, with all the features of 

 the surface ornamentation distinctly shown. 



The protoconch is not preserved, but the first volution remaining, 

 which is probably the first beyond the protoconch, is ornamented by two 

 spirals and faint ribs only. This volution has a diameter of .6 mm. On 

 the next volution three fine spirals appear on the shoulder. Intercalated 

 spirals are first developed on the third volution, and they increase rapidly 

 during subsequent growth until, on the body whorl, those of the fifth 

 order may be counted. The two primary spirals remain of equal strength 

 for eight volutions, but on the later volutions the lower spiral becomes 

 weaker, until it is reduced to the size of a secondary spiral, and the out- 

 line of the whorl is changed from an obtuse angle to approximately a 

 right angle. At intervals on the later volutions of the shell one rib is 

 slightly stronger than the others, and on the body whorl there is one 

 strong varix. A sub-sutural band, as in C. tuberosum, is developed on 

 the ninth and later volutions. Toward the end of the body whorl this 

 band becomes tuberculate, and on the lower slope of this whorl two strong 

 spirals are developed. 



The aperture is elongate oval, with a posterior tooth on the narrow 

 callus of the inner lip. The outer lip is flaring, crenulated by the spirals 

 of the outer surface. The anterior canal is comparatively long. 



Horizon and locality : Recent. Indian Ocean. 

 No. 20126, Columbia University collection. 



Eemarks : Cerithium menkei differs from C. columna in having a 

 thinner shell, finer and more delicate sculpture, broader and less widely 

 spaced ribs. 



The development of the ornamentation of this shell is so closely par- 

 allel to that of C. tuherofium that, taken in connection with the similarity 

 in the form of body and aperture, it leaves no room for doubt that the 



