192 FAMILY GLOBIGERINIDA. 



bi-serial. And in the Verneuilina of D'Orbigny, the arrangement may either remain tri-serial 

 through all the stages of growth, or may become " bulimine," or may give place to a uni-serial 

 succession, in which last case the shape becomes nail-like, so nearly resembling that of some 

 ValvuHntB (^ 221) as only to be distinguishable by the want of the valve characteristic of the 

 latter. The genus ClavuUna of D'Orbigny is made up of these clavuline varieties of ValvuHna 

 and Verneuilina. — The Vuhulina of D'Orbigny (the Grammostomiim of Ehrenberg) , on the other 

 hand, is a very obliquely chambered Texfularia, of which the aperture is a narrow fissure, 

 situated at the most anterior portion of the segment, and lying parallel to the plane of com- 

 pression (Plate XII, fig. 15). This form, too, may become uni-serial. — In all these modifica- 

 tions of the Textularian type, the shell is as frequently arenaceous as it is in the typical 

 Textularia; it is an arenaceous example of the A^erneuiline type, which is figured by Professor 

 Williamson (ex. Figs. 1 36, 1 37) under the designation BuUmiiin areimcea. — Lastly, the Ccuuleina 

 of D'Orbigny is a form in which the chambers present the " globigerine " shape and looseness of 

 aggregation, and are disposed with something of a tri-serial or " verneuiline " arrangement in a 

 turbinoid spire ; the aperture is represented by him (lxxiii) as an elongated fissure biidged over 

 by bars of shell so as to be divided into a row of pores ; but these pores do not represent the 

 true aperture, being only the ordinary pseudopodian passages of the shell- wall, which are pecu- 

 liarlv large and crowded together along the side of the septal line of the newest chamber. In 

 its mode of growth this sub-genus is so closely paralleled by Verneuilina [Bulimina, Egger) 

 py(/mcpa, that it may be questioned whether its distinctive modification is of more than varietal 

 importance. 



321. Affinities. — It is obvious from the intimacy of the relationship between the tri- 

 serial, bi-serial, and uni-serial forms of Textularia, that we are to regard it as essenti- 

 ally a trochoid spire, of which the chambers may be three or two in each turn, or which may 

 straighten itself out by the rectihneal instead of the zig-zag gemmation of its segments. In 

 some of the small loosely-piled varieties of Textularia, there is obviously a very near approach 

 to Glohigerina in the form and disposition of the segments. On the other hand, its larger tri- 

 serial and more trochoid forms tend on the one hand towards certain aberrant forms of the 

 Bulimine series, and on the other towards the arenaceous Vahuinia, to which genus, as already 

 explained, their relationship is extremely close. 



322. Geographical Distribution. — This type is among the most cosmopolitan of Foramini- 

 fera ; presenting itself under some of its forms in sands from all shores and in dredgings from 

 shallow or moderately deep waters. It occurs in greatest abundance, and attains its largest 

 size, in the tropical and warmer temperate seas ; its finest examples ranging from shallow 

 waters to a depth of 200 or 300 fathoms. 



323. Geological Distribution. — The Textularian type can be traced very far back in geo- 

 logical antiquity, being recognisable even in the Palaeozoic period. It becomes much more 

 abundant and varied, however, towards the end of the Secondary period ; its siliceous casts 

 being common in the Greensand, and its shells being frequently met with in the Chalk. It 

 is in the Tertiary strata, however, that its fossil forms present their greatest multiplication 

 and diversity ; and the various modifications of this type at present existing are closely 



