50 ANNAL8 i^fEW YORK ACADEMY OF SCIENCES 



fourth, with a gradual strengthening of the characters already intro- 

 duced. On the seventh volution faint secondary spirals are intercalated 

 between the first two and on the shoulder above the first spiral. The 

 ribs are well defined and extend from suture to suture, about one on each 

 volution being enlarged to form a varix, a feature which persists on all 

 the later whorls. The ninth volution differs only in having an addi- 

 tional faint spiral just below the sutural one. 



An adult individual shows twelve volutions, from which, as shown by 

 comparison with the young, about four volutions in addition to the 

 protoconch have been broken away. On the eleventh volution of this 

 specimen the spirals are five in number, with ribs extending from suture 

 to suture, and separated by interspaces slightly wider than themselves. 

 Although the surface is much dissolved, faint traces of secondary and 

 tertiary spirals may be seen. The strength of all the spirals varies con- 

 siderably, not only with the condition of preservation, but in different 

 individuals similarly preserved. Some individuals show the secondary 

 and tertiary spirals distinctly, while they are hardly visible on others. 

 The spirals of this species, especially on the later volutions, have their 

 upper edge projecting sharply and their lower edge merging into the sur- 

 face of the shell, so that the whorls appear to be made up of overlapping 

 lamellae with their edges turned upward. On the later part of the body 

 volution the spiral just below the suture is broken up into nodes, and the 

 three spirals below the central band become extremely strong. 



The aperture is oval, with a deep anterior canal and a well-defined 

 posterior canal. The callus of the inner lip is narrow but comparatively 

 thick. The outer lip is folded into a series of prominent lobes, which 

 correspond in position with the spirals on the outside of the shell. 



Horizon and localities: Calcaire Grossier (Upper Eocenio). Chaussy and 

 Grignon, Paris Basin. 



No. 20143. Columbia University collection. 



Eemarks : This species begins its life history in a much simpler man- 

 ner than any of the species thus far described, and it is not until the 

 sixth volution that it fully acquires the shoulder, which in recent accel- 

 erated forms begins immediately after the protoconch. The primitive 

 stages preceding the formation of ribs, and with one volution only, have 

 been crowded out of the ontogeny by acceleration in such forms as Ceri- 

 thium adansoni and C. tuberosum. 



Cerithium lameUosum does not continue its development in the direc- 

 tion of C. tuberosum, for, after having acquired intercalated spirals of 

 high orders, it nearly or quite loses them on the adolescent and adult 



