146 CARBONIFEROUS AND PERMIAN FORAM1NIFERA. 



of the genus in geological time, but also in the increased importance it imparts to the 

 Nummulinida in their relation to the Palaeozoic epoch. 



In the living condition Amphistegina is widely distributed. It is found, often in 

 large numbers, in the Coralline and Coral Zones of tropical and subtropical seas, rarely 

 or never in those of temperate latitudes. 



It is common in microzoic deposits of the Tertiary epoch from the Eocene forward, 

 both in Europe and America. Earlier than this it has only been recorded hitherto from 

 a single locality. D'Orbigny, 1 in the ' Tableau Methodique,' gives amongst the species 

 of Amphistegina, one which he names A. Flcuriausi from the Upper Chalk of Maestricht, 

 but without any details as to specific characters. Professor Reuss 2 identifies this with a 

 form found by himself in the same deposit. It is quite open to question whether the 

 fossils described and figured by Professor Reuss ought not to be referred to the allied 

 genus Operculina rather than to Amphistegina ; but on the supposition that they pertain 

 to the latter type, they have been regarded as marking its earliest appearance, so that the 

 discovery of a veritable member of the genus as low down in the geological series as the 

 Carboniferous Limestone adds a long period to its life history. 



AMPHISTEGINA MINUTA, nov. PI. XI, fig. 7. 



Characters. Shell discoidal, lenticular, the two sides nearly equally convex. 

 Margin entire, acute. Chambers very numerous, sinuous. Surface smooth. Diameter 

 ^3 inch (0'77 mm.). 



The unique representative of the genus Amphistegina found in the Carboniferous 

 Limestone, though exhibiting in a striking manner the characters of the type, yields only 

 slender basis for the details of specific description. It resembles d'Orbigny's ' Modele ' 

 (No. 40) of A. vulgaris, but is more Nummuline in general aspect, and the segments are 

 relatively narrower and more numerous. It seems in fact to lie, morphologically, between 

 A. vulgaris and A. Lessonii (Modele No. 98). The shell is, however, smaller than any 

 fossil variety of the genus which has as yet been described. The oldest species, geologically 

 speaking, hitherto recorded (A. Fleuriami, D'Orb.) has a diameter, according to Reuss, 

 of pj of an inch (2'0 mm.) ; D'Orbigny's three Miocene forms range from the same 

 size to of an inch (4* mm.) ; and Dr. Carpenter gives from -^ to y of an inch 

 (1'2 to 3 - 7 mm.) as the range of variation in the various members of the genus. The 

 modification now under notice, in the mature condition, as far as can be told, has only a 



1 'Ann. Sci. Nat.,' 1826, TO!, vii, p. 304, No. 7. 



2 ' Sitzungsb. k. Akad. Wissensch. Wien,' vol. xliv, p. 308, pi. i, figs. 1012. 



