196 FAMILY GLOBIGERINIDA. 



generically, but has even transferred it from his order Helicostegues to that of Entomosteffues, 

 under the influence of a misconception as to the real arrangement of its segments, without 

 giving any other hint of its relationship to Bulimina than that which is afforded by his likening 

 of the form of the entire shell to a minute Bulimus. In our view Rohert'ma is only one of the 

 numerous varieties presented by the B. clcgantissima of D'Orbigny ; in some of which the 

 segments are extremely elongated laterally, and are set very obliquely to the axis of the spire, 

 so that its last turn, consisting of from seven to ten segments, almost completely encloses the 

 preceding, and the whole shell may have much more the form of an OVam than that of a 

 Bulimus (ex, Figs. 13-1, 135) ; whilst in its largest and best developed forms, which occur in 

 Arctic regions, the alternating segments interdigitate with each other. 



332. A general ornamentation of the surface is not common in this type, though we 

 sometimes meet with a longitudinal costation (Plate XII, fig. 19) strongly resembling that of 

 TJmfjerina. This costation may be confined to the earlier segments, the later being quite 

 smooth. The more usual kind of exogenous growth in this type consists in the prolongation 

 of the posterior margin of the segments, in those varieties which are characterised by their back- 

 ward extension; this prolongation may consist in a mere serration, as in the B. maryinata 

 (ex, Figs. 126, 127), or it may go so far as to produce a fringe of long transparent spines, the 

 several segments of the same shell often exhibiting intermediate gradations between these two 

 extreme conditions. In the most spinous varieties the shell itself is generally stronger than 

 in the smooth forms ; on the other hand it is thinnest in the most elongated examples, which 

 seem to be starved out. 



333. We have seen that even in tiie ordinary Bulimine type there is sometimes a 

 tendency to a binary or Textularian alternation of the segments; this, however, is much more 

 marked in certain extremely elongated forms, having a tliin delicate shell that is never 

 arenaceous, and the aperture greatly elongated but still preserving its Bulimine character. 

 To such forms the generic name Virgulina has been applied by D'Orbigny ; but their 

 degree of departure from the Bulimine type is not even of specific importance, as Prof. 

 Williamson has shown himself to have perceived, by ranking them as varieties of his 

 B. piqjoides. — A more decided modification of the Bulimine type is presented by those forms 

 which have been ranked by D'Orbigny in his genus Bolivina, the arrangement of the seg- 

 ments being here regularly bi-serial and alternatmg, as in Textularia ; but the aperture never 

 loses the elongation and the inversion of its lips characteristic of the Bulimine type, and 

 its direction is usually somewhat oblique. In the B. cosfatn of D'Orbigny (Plate XII, fig. 22) 

 there is a set of eight parallel costse, running continuously from one segment to another 

 along the entire length of the shell, giving to it a very peculiar aspect. 



334. Affinities. — It is obvious from what has just preceded, that the affinity of 5«//m/»« to 

 TexMaria is very close ; since Bolivina will rank under one or the other of these generic types, 

 according as we attach the greatest value to the character of the aperture or to jwfo-v of growth., 

 as an indication of natural affinity. That the former has a far stronger claim to acceptance 

 than the latter, appears obvious from the fact that, as we have seen, the plan of growth may 

 vary in unquestionable Bulimina from a continuous succession of segments in a bulimine spire 



