THE FAMILY NUMMULINID.E 243 



marginal caiials conspicuously developed. Loiuer 

 Cretaceous to JRecent. 



Example. — 0. ammonoides^ Gronovius sp. 

 (Nautilus), 'Zooph. Gron.' 1781, p. 282, No. 1220, 

 and p. V. 



A small complanate form with comparatively few 

 chambers and with limbate or thickened sutures. It 

 is found at the present day in fairly shallow water. 

 Pliocene to JRecent. (Plate 13, figs. H, //.) 



Genus Heterostegina, D'Oebigny. 



Test resembling Operculina in general contour ; 

 chambers long and narrow, and divided into chamber- 

 lets ; aperture a row of pores on the outer septal face. 

 Eocene to Becent. 



Example. — H. clepressa, D'Orbigny, 'Ann. Sci. 

 Nat.' vol. vii. 1826, p. 305, pi. xvii. figs. 5-7 ; 

 ' Modele,' No. 99. 



The present species is the type of the genus, and 

 the many variations which have been described 

 as species differ in little from this form. The 

 shell presents itself in the two stages having the 

 large or small initial chamber, in common with many 

 other types of Eoraminifera, and, as is often the 

 case, the small-chambered form is much rarer than 

 the large-chambered form. In the dredgings from 

 Funafuti, where these two conditions were observed, 

 the writer found them in the proportion of about 500 

 of Form A (the megalospheric shell) to 1 of Form B 

 (the microspheric shell). It inhabits moderately 



b2 



