FORAMINIFERA OF THE ATLANTIC OCEAN. 81 



This genus includes those species in which there are three definite 

 stages, the young being triserial, followed by a biserial, and finally 

 a uniserial development. There is a considerable difference in the 

 amount of acceleration of development shown in the various species. 

 Usuall}'- the triserial stage is confined to the very early chambers, the 

 biserial very much reduced or wanting, and the uniserial stage of 

 development making up nearly the whole of the test. In some species, 

 however, the acceleration of development is much less and the stages 

 are held longer. This is seen in such a species as G. gaudryinoides 

 Fornasini,^^ where the biserial stage is distinct. This is much more 

 strikingly shown in ClavuUna primaeva Cushman.^" In this species 

 the biserial stage is kept for nearly half the length of the test. In 

 this respect the species is very unaccelerated and primitive. 



The development shows very clearly the relationships. ClavuUna 

 has evidently been derived from such forms as Verneuilina with its 

 triserial development, through Gaudryina, where a biserial arrange- 

 ment of the chambers characterizes the adult. The paleontological 

 evidence also bears out this relationship, Verneuilina and Gaudryina 

 both being known as far. back as the Lower Cretaceous while the 

 history of ClavuUna so far as known only goes back to the Eocene. 



There are numerous species showing definite geographical distribu- 

 tion. Certain species are limited to warm shallow waters and others 

 are found in deeper cold oceanic areas. 



CLAVUUNA NODOSARIA d'Orbigny. 



ClavuUna nodosaria d'Orbigny, in De la Sagra, Hist. Fie. Pol. Nat. Cuba, 1839, 



•*Foraminiferea," p. 110, pi. 2, tigs. 19, 20.— Cushman, Proc. U. S. Nat. 



Mus., vol. 59, 1921, p. 53, pi. 12, fig. 3; Publ. 311, Carnegie Inst. Wash., 1922, 



p. 30, pi. 3, figs. 1, 2. 

 Textularia gibba d'Orbigny, forma Bigenerina Goes, Kongl. Svensk. Vet. 



Akad. Hand]., vol. 19, No. 4, 1882, p. 79, pi. 5, figs. 162-164 [?]. 

 ClavuUna laevigata Goes, Kongl. Svensk. Vet. Akad. Handl., vol. 25, No. 9, 1893, 



p. 40, pi. 8, figs. 356-367. 

 ClavuUna communis Goes (not d'Orbigny) (part), Bull. Mus. Comp. Zool., vol. 



29, 1896, p. 36, pi. 4, figs. 9-15 [?]. 



DescripHon.— Test small, elongate, subcylmdrical, early portion 

 triserial, more or less triangular, the angles rounded, succeeding 

 portion uniserial, hardly if at all tapering, circular in transverse 

 section; chambers fairly numerous, those of the early portion less 

 distinct than those of the later portion, those of the uniserial portion 

 somewhat inflated; sutures distmct, slightly depressed, wall finely 

 arenaceous, smoothly finished on the exterior; aperture one or more 

 usually circular pores on the terminal face of the last-formed cham- 

 ber; color light yellowish-gray. 



Length usually less than 1 mm. 



» Mem. Acad. Sci. Bologna, ser. 6, vol. 10, 1903, p. 313, pi. O, fiR. 21. 

 M Proc. U. S. Nat. Mus., vol. 44, 1913, p. 635, pi. SO, figs. 4, 5. 



