53 ANNALS NEW YORK ACADEMY OF SCIENCES 



The aperture is oval, with a long columella and poorly formed siphonal 

 canal. 'No callus is present on the inner lip, and the outer lip is too 

 much broken to determine its character. 



HoBizoN AND LOCALixy : Calcairc grossier. Grignon, Paris Basin. 

 No. 2564, Museum of Comparative Zoology collection. 



Eemarks: The absence of a callus on the inner lip and the poorly 

 formed siphonal canal accompanying a surface ornamentation character- 

 istic of young Cerithium seem to indicate that these specimens are young 

 individuals. They are referred to C. inabsoJutum on account of the elon- 

 gation of the lower part of the aperture and the character of the orna- 

 mentation, which seems to correspond with that described for the species. 

 Whether or not the specific identification is correct, they belong undoubt- 

 edly to the genus CeritJiium sens. str. 



Cerithium calcitrapoides Lamarck 



1804. Cerithium calcitrapoides Lamarck, Ann. du Mus. Nat. d'hist. naturelle 

 de Paris. Ill, 274. 



1824. Ceritliium calcitrapoides Deshayes, Desc. des coquilles foss. des envi- 

 rons de Paris, 347, pi. 46, figs. 18, 19, 23. 



1906. Batillaria calcitrapoides Cossmann, Essais de Pal6oconch. Comp., VII, 

 134. 



Measurements : Length, 50 mm. ; greatest diameter, 18 mm. ; apical angle, 

 25° ; sutural angle, 87°. 



The youngest volution studied has an ornamentation of one spiral 

 only. On the next volution a second spiral appears above the first, and 

 on the fourth volution of those preserved, the two spirals are crossed by 

 ribs, but it is not until the fifth volution that the two spirals become 

 equal in strength. At this stage the shell has the shoulder characteristic 

 of Cerithium, with two equal spirals crossed by ribs. On the seventh 

 volution a spiral is intercalated between the two primary spirals, and fine 

 ones appear also on the shoulder and on the lower slope of the whorl. On 

 the ninth volution the lower primary spiral has become weaker than the 

 upper, a tendency which increases until, on the twelfth and later volu- 

 tions, the lower primary spiral is reduced to the size of the secondary 

 ones, and the upper spiral forms the projecting margin of a sharply 

 angled volution. 



The aperture is elongate oval, with a thick callus on the inner lip and 

 short, widely open canal. The outer lip is slightly crenulated. 



Horizon and localities : Calcaire grossier. Sables Moyens. Grignon and 

 many other localities in the Paris Basin. 

 No. 3377, American Museum collection. 



