THE FAMILY LAGENIDiE 191) 



specimens in the Middle Hils Clay of North Ger- 

 many (Aptian stage). (Plate 10, lig. V.) 



Sub-family 3. Polymoephinin^. 



Segments arranged spirally or irregularly around 

 the long axis ; rarely biserial and alternate. 



Genus Polymorpliina, D'Oebigny. 



Segments biserial or triserial or irregularly spiral. 

 Aperture radiate. Trias to Recent. 



Example. — P. gihha, D'Orbigny, ' Ann. Sci. Nat.' 

 vol. vii. 1826, p. 266, No. 20 ; — Modele, No. 63. 



This species has an almost globular test, generally 

 with three chambers visible on one of the surfaces. 

 The suture lines are only faintly marked on the 

 shell-surface. 



P. gibha first makes its appearance as a fossil in 

 beds of Oolitic age, and it is found in all succeeding 

 formations to the present day. It is a well-distributed 

 species both geographically and bathymetrically. 

 (Plate 11, fig. A.) 



Dimorphous Form. 



Genus Dimorpliina.^ D'Orbigny. 



Early chambers Polymorphine, later ones Nodo- 

 sarian. 



Example. — D. tnberosa, D'Orbigny, 'Ann. Sci. 

 Nat.' vol. vii. 1826, p. 264, No. 1 ; Modele, No. 60. 



The shell of this species is elongate, subcylindrica], 



