254 Messrs. R. B. Newton and R. Holland on some 



the general view of writers on Nummulites has been that ex- 

 pressed by the diverse nomenclature. Of late years, however, 

 considerable attention has been given to the study of the 

 initial and immediately succeeding chambers of the shells of 

 the Foraminifera, and notably by MM. Schlumberger, 

 Munier-Chalmas, and Van den Broeck. Mr. J. J. Lister, too, 

 has closely studied the life-history of Polystomella, a genus 

 nearly allied to Nummulites. The result of the researches of 

 these and other observers * is to show that many species of 

 Foraminifera are dimorphic, and it seems to be probable, in 

 the light of Mr. Lister's observations, that the coupled forms 

 of Nummulites represent alternate generations of one species. 

 In any case it seems to be desirable that the nomenclature 

 should express relationship between the companion forms, 

 and it appears that there is more advantage, in the present 

 state of our knowledge, in considering paired forms as 

 varieties of one species than as specifically distinct. We 

 therefore, following the rule of M. Schlumberger as regards 

 other Foraminifera, designate this large form with minute 

 initial chamber N. javanus, form B, and the smaller com- 

 panion with large initial chamber N. javanus, form A. 



2. Nummulites javanus, Verbeek, form A. 

 (PI. IX. figs. 4 & 5.) 



Nummulites baguelends, Verbeek (pars), Nat. Tijdsch. Nederl. -Indie, 

 1891, vol. li. p. 107 ; Description g£ologique de Java et Madoura, 

 1896, vol. i. pi. iii. fig. 75, pi. vi. figs. 81-85, vol. ii. p. 1148. 



Shell lenticular; regularly swollen at the centre; edge 

 obtuse ; surface probably smooth ; " filets cloisonnaires " 

 subreticulate. The mean dimensions of our specimens are 

 3*2 millim. in width by 1*8 millim. in thickness, but these 

 measurements are probably rather less than the actual for 

 the reason given in the description of the form B. The 

 number of convolutions is usually 4 or 5. We have not 

 found in our preparations any good horizontal sections, but 

 we have enough to show that the size and irregular shape of 

 the initial chamber, the generally semilunar shape of the first 

 succeeding chamber, the dimensions of the chambers in the 

 spire, and the closing-in of the later convolutions constitute a 



* Bull. Soc. G<5ol. France, ser. 3, vol. viii. 1880, p. 300; Comptes 

 Rendu?, vol. xcvi. 1883, pp. 862-866 and pp. 1598-1601 ; Ann. & Mag. 

 Nat. Hist. ser. 3, vol. xi. 1883, pp. 340, 341 ; Bull, des Stances de la Soc. 

 roy. Malacol. de Belgique, 1893, torn, xxviii. ; Phil. Trans, vol. 186, 1895, 

 pp. 401-453 ; Proc. Camb. Philosophical Soc. 1897, vol. ix. part 5, 

 pp. 236-240. See also T. R. Jones, Ann. & Mag. Nat. Hist. 1894, ser. 6, 

 vol. xiv. pp. 401-407. 



