Nomenclature of the Foraminifera. 179 



figures of the very protean Truncatulina variabilis, D'Orb., a 

 Mediterranean form exactly intermediate between the tropical 

 Planorbulina vulgaris and Nautilus farctus, which we find recent 

 in the Mediterranean and other seas. This noble work also 

 affords numerous striking illustrations of the other varietal forms, 

 differing in their extremes, yet blending by gentle gradations. 



Nautilus farctus is a Planorbuline Rotalia, and is the type of 

 the species comprehending the above-mentioned and many other 

 varieties. Like Rotalia repanda, it represents the medium 

 between extreme conditions ; its discoidal growth and its high 

 and well stuffed-out chambers give it good title to its name and 

 systematic place. Whilst arrested, as compared with some of 

 the extravagantly grown forms, it is much better developed than 

 many of the varieties enumerated, presents indications of all its 

 essential specific features, and keeps its subgeneric characters 

 better than the trochiform varieties, some of which become, as it 

 were, isomorphs of Rotalia proper, others of Nonionina. 



29. Nautilus tuberosus. Page 111, pi. 20. figs. g-k. "Fossil: 

 Coroncina." 



This is a variety of Planorbulina farcta, with many chambers 

 irregularly set on, and mostly narrow. This PI. tuberosa has 

 the biconvex form which chiefly characterizes D'Orbigny's Ano- 

 malina, and is intermediate to his A. Badenensis and A. Austriaca. 

 This tuberose variety may be said either to represent an early 

 stage of Planorbulina vulgaris, or to be a neatly growing and 

 nearly symmetrical modification of Truncatulina variabilis. Like 

 P. far eta, this variety is very common in the Mediterranean and 

 other warm seas, and occurs in Tertiary deposits. 



30. Nautilus planatus. Page 91. Three varieties. "Recent: 

 Leghorn coast, Tuscany/' 



Var. a. PI. 16. figs, a-c (i, section). "Schroter, Neue 

 Literat. d. Naturgesch. vol. i. p. 314, pi. 1. fig. 7." 



Var. . PL 16. figs. d-f. 



Var. y. PI. 16. figs, g, h. 



This is ' ' le Penerople aumusse " (the Peneroplis planatus} of 

 Denys de Montfort, and is a distinctly specific type of one of the 

 opake-shelled Foraminifers. Commencing with a primordial 

 double chamber, like that of the Miliola, Orbiculina, and Orbito- 

 lites, it soon takes on a Nautiloid growth ; the aperture, at first 

 single, margined, and irregular, soon becomes more irregularly 

 trilobate in the successively enlarging triangular septal faces 

 (as in Dendritina, where it is arborescent) ; in a further stage of 

 the shell, the newer chambers are flat, narrow, and transversely 

 long, spreading out with widening curve, keeping a Nautiloid 

 outline, as in var. a; becoming auricular or bonnet-shaped, as 

 in var. (3 j or showing some modifications of the above, arising 

 from an irregular periodicity of growth, as in var. 7. In other 



