210 FAMILY GLOBIGERINIDA. 



Genus XV.— PuLViNULiNA (Plate XIII, figs. 4—6 ; and Williamson, Figs. 98—103). 



364. External Characters and Internal Structure. — The group of Rotaline forms wliicli are 

 associated in this genus consists of those which accord more or less closely with its type, — the 

 Nautilus repandus of Fichtel and Moll, the Flacentula pulvinata of Lamarck, the RotaUa or 

 Uotalina repanda of later systematists, — in the freedom of growth and in the fineness of the 

 porosity of its shell ; by both of which characters, but especially by the second, it is distin- 

 guished from Discorhbia. The shells of this genus are usually composed of from seven to 

 twenty-six segments of variable convexity, somewhat loosely aggregated in a depressed 

 turbinoid spire, so as to have a biconvex form with the upper side thickest, and an angular 

 or sub-carinate margin (Fig. XXXII, A, p. 201). On the under side there is a large umbilical 

 space, which may either remain open (ex, Fig. 102), or may be partially or completely filled 

 by exogenous deposit. The segments usually undergo a rapid elongation ; and sometimes 

 the later ones spread themselves out irregularly (ex. Figs. 95 — 100). An elongation takes 

 place in the septal plane, in accordance with the extension of the chambers ; and in such 

 cases it tends to become flattened (ex, Fig. 95), and is very commonly punched with large 

 " orbuline" foramina. The aperture is usually a large slit at the base of tlie umbilical margin 

 of the septal plane ; and is frequently still further enlarged by irregular deficiencies at its 

 septal edge. In the typical Puhinulincs the exogenous deposit is chiefly confined to the septal 

 bands, which it often raises into ridges so as to produce a strong " limbation ;" but it may 

 also roughen the general surface with minute granulations. Some of the most oblong- 

 varieties, as the Eolalina ohlonya of Williamson (ex, p. 51) were included by D'Orbigny in 

 his genus Valvulina. 



365. The expanded form of this type may give place to one more contracted, in which 

 the segments are more compactly arranged, so as to produce by their aggregation a thick 

 conical shell, of which the external walls are " flush." In this variety the upper surface 

 usually receives a considerable amount of exogenous deposit, which forms a strong " limbation" 

 on the septal lines (ox, Figs. 101, 103), and covers the outer walls of the chambers with 

 large closely-set granules ; and the aperture passes into the condition of a notch. Tlie limba- 

 tion and granulation attain their maximum in the conus-shaped P. caracolla of the Oolite, 

 Gault, and Chalk-marl, in which the limbation is stronger than in any other Rotalines, the 

 faces of the chambers often lying deep between wall-like ridges both above and below. The 

 variety known as Botalia Ilenardii is a common deep-sea form of PidvinuUna, flattish, limbate, 

 and granular ; and tliis is sometimes accompanied by the E. elegans vel PartscMana (lxxiii), 

 a large flush-chambered shell, with a prominent umbo formed by a mass of exogenous deposit, 

 which variety ranges also into shallower water. In some other varieties allied to B. Menardii 

 the hmbation is wanting; the septal bands being flush with the surface, or being even furrowed. 

 In the P. Schreibersii and allied varieties the limbation is but faint, or is altogether wanting, 

 on the upper surface of the shell; whilst on the under surface there is a strong astral 

 limbation proceeding from the exogenous deposit which occupies the umbilical vestibule. 



