146 FAMILY LITUOLTDA. 



Genm III.— Valvulina (Plate XI, figs. 15—26). 



218. Histor//. — The genus Valvulina was established by D'Orbigny (lxix) to compre- 

 hend a group of multilocular shells, some fossil and some recent, which are distinguished by 

 their turbinoid mode of growth, and by the partial occlusion of the single aperture of each 

 chamber by a peculiar valve or tongue that projects from the umbilicus. The genus has 

 of late been carefully studied by Messrs. Parker and Rupert Jones (lxxix) ; and the account 

 which I give of it may be considered as virtually theirs, while the illustrations of it given 

 in Plate XI are drawn from typical specimens with which they have kindly furnished me. 

 All the forms which they consider properly to belong to this genus are arenaceous ; but 

 several were included within it by D'Orbigny, which they consider to be varieties of Rotalia 

 turbo and R. repanda. 



219. External Characters and Internal Structure. — ^The impossibility of drawing definite 

 lines of demarcation between even the primary groups of Foraminifera is remarkably shown 

 in the type before us ; shice, although its shell is constantly arenaceous and is (for the most 

 part) jisrr/c/'icft//^ imperforate, yet it is formed on the basis of a perforated vitreous lamina, 

 which is sometimes brought into view at the apex of the spire by the rubbing away of the 

 arenaceous incrustation, and which also occasionally displays itself (especially in the large 

 depressed variety) in the walls of the last-formed chambers (fig. 22), these having not yet been 

 thickened to the same degree as the preceding by the aggregation of foreign particles. Thus 

 in regard to the fundamental texture of its shell, Valvulina is obviously related to the vitreous 

 series ; and we shall see that to certain genera of that series its affinity in general characters 

 is so close, as to render doubtful the propriety of its separation from them. But whilst the 

 shells of those genera are often so arenaceous as strongly to resemble those of Valvulina, the 

 fact that they are often entirely free from arenaceous incrustation shows the animal to possess 

 the power of forming a regular shell of the ordinary vitreous substance; and their pores may 

 generally, if not always, be distinguished, on a careful examination, in the intervals of the 

 attached sand-grains ; so that the exit of their pseudopodia is not interfered with. In Valvu- 

 lina, on the other hand, the arenaceous incrustation consists not merely of sand-grains 

 attached to the proper testaceous lamella, but, as in the case of Lituola and Trocliammina, of 

 a cement formed of very fine particles, in which larger grains are imbedded ; and b)' this 

 cement, wherever it is present in any amount, the perforations are so effectually closed-up, 

 that the shell becomes actually imperforate, excepting in the wall of its last-formed chambers. 

 Hence we have considered that the place of this genus is rather in the Sub-Order Imperforata 

 than in that of Perforata; but it would, perhaps, be more correct to assign to it an indepen- 

 dent position as the connecting link between the two. 



220. It is more easy in Valvulina than in the two preceding genera to refer all the 

 principal modifications to one central type ; the Valvulina triangularis of D'Orbigny being the 

 form of which the rest may be regarded as varieties. This is a triserial, three-sided, pyra- 

 midal shell (Plate XI, fig. 15), having three chambers in every turn of its spire, and presenting 



