Tertiary For aminif era from Borneo. 253 



horizontal plane must be, because no strictly horizontal plane 

 will exactly pass through the middle of every chamber in the 

 median section. The central chamber is invisible. 



These large Nummulites are undoubtedly identical with 

 one or other of the four varieties of N. javanus described by 

 Dr. Verbeek, and the species is closely related to the well- 

 known N. l&vigata of Europe. Dr. Verbeek may be cited in 

 support of this view as to the affinities of the species. He 

 describes as A 7 , laevigata one of his Javan Nummulites, and 

 goes on to say (op. cit. p. 1152) : — " La seule difference entre 

 celte espece et la N. laevigata d'Europe (notamment telle que 

 Carpenter la decrit et la repre"sente dans le Quart. Journ. of 

 the Geo!. Soc. vol. vi. 1850, pi. iii. fig. 2, car la description 

 et les figures de cette espece par d'Archiac ne sont pas toujours 

 exactes), c'est l'aspect plus ponctue" de la surface et le nombre 

 un pen plus considerable des tours de spire pour une meme 

 rayon. . . . Notre espece a aussi beaucoup d'analogie avec 

 le N. javanus var. h, tant pour le nombre des tours de spire 

 que pour celui des loges, de sorte qu?il faut peut-etre la con- 

 sidSrer comme une 5' varidte" de notre N. javanus a cloisons 

 moins arquees et a piliers plus Spat's." 



The figure by Caipenter to which Dr. Verbeek refers above 

 is that of a A 7 , laevigata from the Bracklesham Beds in Sussex, 

 which differs very considerably from the typical N. laevigata 

 of the Paris Basin and Belgium— differs,, in fact, as widely as 

 other Nummulites which have been ranked as separate 

 species. N. javanus departs from the typical N. laevigata in 

 a somewhat opposite direction, but hardly perhaps more 

 widely. That the Bornean specimens are very close allies 

 of A 7 , laevigata is further shown by their association with a 

 form having a large initial chamber and bearing a strong 

 resemblance to N. Lamarcki, the European companion of 

 N. laevigata. 



This association of Nummulites, first indicated by 

 Messrs. Parker and Jones (Ann. & Mag. Nat. Hist. ser. 3, 

 vol. viii. 1861, p. 233), is a very well-known phenomenon. 

 Every student of these fascinating organisms is aware that 

 Nummulites almost always, if not invariably, occur in pairs 

 of so-called " species." One of the members of the couple is 

 generally larger than its fellow, and has always a very minute 

 or even invisible initial chamber, while the other member, 

 which never attains a large size, is distinguished by the 

 possession of a comparatively large initial chamber. Each 

 member of such a couple has been looked upon as a distinct 

 species, and has been named accordingly. The propriety of 

 the distinction has been questioned by several authors, but 



