H. B. Brady — Fossil Foram'mifera of Sumatra. 533 



most fully represented excepting Orbitoicles, as far as number of 

 specimens goes, is the genus Operculum. The Operculinai are in two 

 sets, the more numerous series, containing also the finer examples, 

 from the Coralline Limestone of Nias Island ; the smaller one from 

 the West Coast of Sumatra. Of the larger examples, Figs. 1, a, b, c, 

 Plate XIII. are fairly. representative. They may be assigned without 

 hesitation to Operculina granulosa, Leymerie, a variety differing from 

 the typical 0. complanata, Defrance, not only in its more or less 

 granulate or beaded surface, but in the slower and more gradual in- 

 crease in breadth of the spiral band of chambers. The specimens of 

 the less numerous set are smaller in size, and their characters are 

 much less strongly marked. They bear some resemblance to the 

 modification figured by Leymerie (loc. cit. fig. 11, a, b) under the 

 name 0. ammonca ; but there can be little doubt that the differences 

 in minor particulars are dependent on mere external circumstances 

 either of life, or in the process of fossil ization ; at any rate there 

 seems no substantial basis for their specific separation. 



The finer specimens of 0. granulosa from Nias Island have a 

 diameter of -J- inch (4-5 mm.), and consist of about five moderately 

 broad convolutions, the individual chambers being very narrow and 

 numerous. The primordial chamber is minute, as is commonly 

 the case in the Operculine type ; but there is considerable thickening 

 of the shell-wall, especially near the centre, shown externally by 

 a more or less prominent umbo. 



Operculina granulosa is a well-known species occurring in the 

 earlier Tertiary beds of Europe in company with fossil Nammulinoe. 



Localities — The precise habitats of these Eastern specimens of 

 Operculina are the Tertiary Limestone of Nias Island, where they 

 are found in company with Corals and Nummulites, and the Marl- 

 sandstone, of an earlier Tertiary age, in the Padang Highlands on 

 the West Coast of Sumatra. 



2. NuMMULixA variolahia (Sowerby). PL XIII. Figs. 2, a, b, c, 



3, a, b, c. 

 Nummularia variolaria, Sowerby, 1829, Mineral Conchology, 



vol. vi. p. 76, pi. 838, fig. 3. 

 Nummulites variolaria, D'Archiac et Haime, 1853, Descr. Anim. 



foss. Groupe numm, de l'lnde, p. 116, pi. 9, figs. 13, a — g. 



A set of minute Nummulites (labelled " small "), of which Figs. 

 2, a, b, c, are examples, and another series (marked " middle-sized ") 

 represented by Figs. 3, a, b, c. may both be assigned to the same 

 species — N. variolaria. The smaller ones are about T * T inch (1* mm.) 

 in diameter, and consist of about three convolutions, of which the 

 third possesses, on the average, sixteen chambers. The primordial 

 chainber is ^-^ inch (0*1 mm.) in diameter. The larger specimens 

 average about T ' T inch (2-0 mm.) in diameter, and have four or more 

 convolutions, the outermost composed of about nineteen segments ; 

 the primordial chamber is of the same size as in the smaller ones. 

 The proportionate thickness is much the same in the two cases, save 



