OPERCULINA. 361 



Characters. — Shell lenticular, unequally biconvex, umbonate ; chambers nume- 

 rous ; septal lines sinuous on the upper, curved and astral on the lower surface ; 

 margin acute; surface smooth. 



Distribution. — Amphistegina vulgaris (including Lessonii) is mostly confined to 

 tropical and subtropical seas ; and, as a rule, does not extend to depths beyond 

 400 fathoms, and is most common at depths of less than 30 fathoms. Rare 

 specimens have, nevertheless, been recorded from much greater depths — 1750 

 fathoms by the ' Challenger,' and 2714 fathoms (A. Hauerina) by the ' Gazelle.' 



Dr. A. Goes found this species at 20, 100, 300, and 1000 fathoms in the 

 Caribbean Sea. 



The genus in the fossil condition has been recorded from the Carboniferous 

 of Bristol (H. B. Brady) ; the species from the Eocene of France (Calcaire 

 Grossier) ; of Bavaria (Nummulitic beds of the Traunstein, Ehrenberg) ; and 

 (?) of Java (Orbitoidal Limestone, Ehrenberg). 



It is, perhaps, the most characteristic Foraminifer of the Miocene deposits 

 generally ; and it has been found in the Pliocene of many localities, especially in 

 Italy, also at St. Erth. We include Amphistegina vulgaris as a constituent of the 

 Crag rhizopodal fauna with some reservation. The specimens from Sudbourne 

 found by Mr. S. V. Wood seem to carry evidence of having been washed from 

 some earlier formation. 



Genus 2. — Operculina, d'Orbigny, 1826. 



Carpenter, Introd. Foram., 1862,^9. 247 — 262, pi. xvii ; Brady, Report 

 'Challenger,' 1884,^. 76, 742. 



Nautilus, Gronovius, Schroeter, Gmelin. 



Lenticulites, Defrance, Basterot. 



Opeeculina, d'Orbigny, JBronn, Michelotti, von Reuss, Leymerie, Cornuel, Riiti- 

 meyer, d'Archiac and BZaime, Carter, Parker and Jones, Carpenter, 

 Brady, M. Sars, Kaufmann, von Haniken, Vine, Quensfedt, 

 Schafhautl, Schauroth, von Giimbel, Schwager, Michelotti, Brown, 

 T. Wright, von Zittel, Locard, Steinmann, Pictet, Mayer, M. 

 Chalmas, Galeotti, Terquem, Ansted, Kolliker, Williamson, 

 Figuier, Biitschli, Woodward and Thomas, &c. 



Amphistegina, d'Orbigny, von Reuss. 



Nonionina, Williamson, Fischer. 



Nummulina, Parker and Jones. 



General Characters. — Shell free, equilateral, piano-spiral; formed of a regular 

 spire, the successive convolutions of which are in close contact without over- 



