ii4 



J. J. LISTEil. 



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 Kupert Jones, dated 

 Oct. 1, 1879 (19 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. 



Biloculina depressa, d'Oee. Sections of the shell— 



A. Of the megalospherio form. (Megalosphere 200-400 /i.) 



B. Of the microspherio form. (Microsphere 20 /u,.) The two terminal 

 chambers are omitted in B. 



(Munieb-Chalmas and Schlumberger, 25.) 



