OF THE SUB-ORDER PERFORATA. 151 



by an aggregation of globular segments that arc united to each other by external adhesion 

 only, each segment possessing its own separate aperture. The shelly walls of the segments 

 are composed of a coarsely porous substance, having little or no surface- ornamentation ; and 

 the aperture which leads to their cavity is a simple fissure, usually crescentic in form, 

 without cither prominence or lip. Now this simple " globigerine " type may develope 

 itself, as we shall hereafter see, into a very remarkable form {Carpenter in), in which, without 

 any departure from the essential characters of the original, a high degree of complexity is 

 superinduced by the enlargement and sub-division of the later chambers (which completely 

 include the earlier growth), and by the peculiar provision that is nevertheless made for the 

 maintenance of the direct communication between each chamber and the exterior. But 

 whilst this is, so to speak, a lateral offset, 'the tendency to a really higher elevation shows 

 itself in the more intimate union of the chambers, which no longer have separate external 

 apertures, but open sequentially, each into the one that succeeds it, the last alone having an 

 external aperture. Now such a series of globigerine chambers, budded forth alternately on 

 the two sides of a linear axis, becomes a Tcxfularia ; whilst if the succession follows the course 

 of a spire resembling that of a Bul.imus, a Bulimina is formed. These types accord closely 

 with Gloherhpna in the characters of their individual segments ; and their low grade of 

 development is marked, like that of the Laycnida, by the incompleteness of the posterior wall 

 of the new segment whenever the anterior wall of its predecessor can be used to complete the 

 enclosure of the chamber, and by the entire absence both of " intermediate skeleton " and of 

 " canal-system." Yet in some large forms of Teninlaria we find — as in Carpentcria — a partial 

 subdivision of the chambers into chamberlets, which is decidedly a character of elevation ; but 

 there is no further progress in that direction, such forms marking the culmination of the 

 Textularian type. 



230. Reverting again to Glohigcrhui, we see in the turbinoid plan on which its chambers 

 are disposed an obvious foreshadowing of the turbinoid spire which is the essential character- 

 istic of the Botalian series ; so that nothing more is needed to convert a Ghbigerina into a 

 Rofalia, than that its chambers shall open successively each into the next, the last alone 

 opening externally. We shall find ourselves required, by the absence of any natural lines of 

 demarcation, to group together, under the generic name Bofalma, a. series of forms that present 

 very wide diversities in grade of development; the simplest presenting but a slight advance 

 upon Glohigerina ; whilst the most elaborate exhibit the special features of the perforated 

 series — namely, the double septum between the chambers, the intermediate skeleton, and the 

 canal-system — in a highly characteristic aspect; the last two of these peculiarities being 

 nowhere more conspicuous than in Calcarina, which is little else than a modified 

 Botalia. But whilst the development of the central stem thus takes place on the original 

 type, that of the branches or oS'sets may follow a very different course. Thus there are low 

 forms of Bofalia repanda, whose spire is so much flattened out, and whose chambers are so 

 greatly elongated, that they come to resemble what a SjArillina would be, if its one continuous 

 vermiculate chamber were partially divided by transverse constrictions. In some of these we 

 find a tendency to the obliteration of the regular spiral mode of increase by a " wild " growth 

 of the marginal chambers ; but this substitution of an indefinite for a definite plan is more 

 characteristically seen in the Plauorbtdine forms, which, commencing on the regular Rotalian 



