Nomenclature of the Foraminifera. 103 



are carried to greater extent in the following varieties. This 

 variety is not common ; our best specimens are from the Arctic 

 Seas. 



6. Nautilus striatopunctatus. Page 61, pi. 9. figs. a-c. 

 " Recent : Red Sea*." A smooth round-edged Nonionine shell, 

 variable in its thickness and in the number of bridges over the 

 septal spaces. Its aperture varies from the simple cross-slit to 

 the cribriform plate. Here the Nonionine character is merged 

 in that of Polystomella, the septal lines being more or less regu- 

 larly bridged over, though often so minutely as to escape casual 

 observation. When more developed, these bridgings of the 

 septal lines produce not only linear pits, but sometimes a double 

 row of septal galleries. In the P. gibba of Schultze the septal 

 bridges are well developed, and a further growth of exogenous 

 matter takes place over the whole shell, in the form of elegant 

 sinuous patches of transparent calcareous granulations. A still 

 greater modification of the surface obtains in Polystomella crispa 

 and its allies, presently to be noticed. 



P. striatopunctata sometimes has the simple crescentic aper- 

 ture of Nonionina ; but this is often subdivided by calcareous 

 bars, and so becomes the cribriform septal plane of Polystomella. 

 It may be either umbilicate or umbonate ; and the umbo may 

 be granulated, and so afford a gradation into Nonionina granosa, 

 D'Orb. 



Polystomella, indeed, is but a more complex form of Nonio- 

 nina. They belong to one generic group ; and indeed we seem 

 to have but one, or at most two, species here. Some of the 

 Nonionina (of the N. spharoides type) are probably of a different 

 specific group. As two subspecies, the Nonionina asterizans and 

 Polystomella crispa may be retained in nomenclature with advan- 

 tage N. asterizans being the central form of one, and P. crispa 

 that of the other; but Polystomella is the true leading form. 



Nonionina striatopunctata occurs in shore-sand nearly every- 

 where, especially in the Arctic Seas, where it attains its greatest 

 size, and is accompanied by N. Faba, N. Scapha, and N. stelli- 

 fera. It is found fossil in the Upper Tertiaries. 



Ehrenberg has well figured, with natural colours, some living 

 specimens of N. striatopunctata (under the name of Geoponus 

 Stella-borealis), from Cuxhaven, in the ( Abhandl. Akad. Berlin, 

 1839' (1841), pi. 1. figs. a-g. 



7. Nautilus ambiguus. Page 62, pi. 9. figs. d-f. " Recent : 

 Red Seaf." This is a somewhat flat Polystomella, slightly 

 umbonate, with the septal spaces open, rendering the chambers 



* In sand obtained from large shells, and given to the authors by 

 Spengler. 

 t In sea-sand from shells, given by Spengler. 



