Il4 



J. J. LISTEtt. 



The existence of the two closely associated forms had also 

 been previously recognized by DE Hantken and de la Harpe. 

 De la Harpe, in a letter to Professor Rupert Jones, dated 

 Oct. 1, 1879 (1.9 a, p. 91), states a "general law of the distri- 

 bution of Nummulites, according to which the characteristic 

 species of a bed are always two of the same zoologic group, 

 of which the larger has no central chamber " (distinguishable by 

 a lens) "and the smaller always has one." In illustration eight 

 pairs of species thus associated are given. 



In 1881, DE LA Harpe (15), expressing his own views and 

 those of de Hantken, commented on Munier-Chalmas' paper. 



Blloculina depressa, d'Orb. Sections of the shell— 



A. Of the megalospheric form. (Megalosphere 200-400 fi.) 



B. Of the microspheric form. (Microsphere 20 fx.) The two terminal 

 chambers are omitted in B. 



(Munier-Chal5ias and Schlumbergeb, 25.) 



