184 FAMILY GLOBIGERINIDA. 



the Gault, in which it is small and not abundant. It is, however, extremely abundant in the 

 Chalk-marl and Chalk, forming a considerable proportion of some specimens of those deposits ; 

 and it occurs in nearly all Tertiary beds of deep-sea origin,- — the Vienna and Sub-Apennine 

 Tertiaries yielding it iii greater amount than the basins of Paris and Bordeaux. 



Genus V.— Pullenia (Plate XII, fig. 12). 



299. Histori/.— The generic designation Pullenia is applied by Messrs. Parker and 

 Rupert Jones to a minute form which has been represented by M. D'Orbigny (Modeles, No. 

 43) under the name of Nonionina sphceroides, and has been subsequently described by him 

 (lxxiii) under the name of N. hdloides. It differs so widely from the ordinary Nonionina 

 (which we shall hereafter see to be low forms of Poli/sfomella), and presents such features of 

 approximation to Globigerina, as to justify its being ranked as an aberrant form of the group of 

 which the latter is the type ; whilst it is differentiated from all other forms at present known 

 by characters that are of sufficient importance to justify its being ranked as a distinct genus. 

 The place here assigned to it will be found to harmonise in a remarkable manner with the 

 peculiarity of its geographical distribution. 



300. External Characters and Infernal Structure.— The shell of Tulhnia has a globose 



form, the distance between its two poles being nearly or quite as great as the diameter of the 



spire (Plate XII, fig. 12). It is formed of a series of segments following one another in a 



symmetrical or nautiloid spiral, the number of these segments in each turn of the spire being 



usually four or five; each whorl is normally invested by that which succeeds it, the chambers 



of the latter being prolonged on either side to the centre of the spire ; and the last chamber 



is usually large, occupying about one third of the lateral aspect of the spire. The septal plane 



is a narrow crescent (fig. 12, a); and the aperture is a very elongated fissure, extending almost 



from one point of that crescent to theother. The segments are in general but slightly convex, 



without any considerable depressions at their junctions ; but sometimes they are turgid or 



vesicular, and obliquely coiled, like the chambers of Globigerina ; and it may then happen 



that they do not so far extend themselves over the preceding whorl as to conceal it, so that 



the whole spire remains visible. These minute shells are extremely glassy in their texture, 



and their pores are fine. They are among the smallest Polythalamia at present known ; their 



diameter averaging l-50th and never exceeding l-30th of an inch. 



301. Affinities. — This type is related to Globigerina in the simphcity of its structure, and 

 in the occasionally globigerine character of its chambers, as well as in the wideness of their 

 aperture ; whilst among true Globigerina there are some forms which approach it in mode of 

 growth. On the other hand, it is related to Nonionina in its plan of growth, and in the com- 

 parative fineness of its porosity. 



302. Geograpliical and Geological Distribution. — The home of this genus — like that of 

 Globigerina, but unlike that of Nonionina — is in the deep seas, especially those of warm 



