180 FAMILY GLOBIGERINIDA. 



287. Geological Distribution. — This genus, so far as is at present known, was limited to 

 the earlier portion of the Tertiary period ; making its first appearance in the Eocene deposits 

 of Grignon and Hauteville, in which it is extremely abundant; and lingering, under its 

 attenuated forms, in the Miocene of St. Domingo. In no deposits of subsequent date has 

 it been recognised. 



Gems III.— Spirillina (Wilhamson, Figs. 202, 204). 



288. History. — Through the marked isomorphism between this genus and Cornuspira 

 (^ 82), it cannot be affirmed with confidence to which type we are to refer the figures and descrip- 

 tions of minute spiral monothalamous shells given by Soldani and after him by other authors, 

 who did not clearly distinguish between such as are imperforate and porcellanous, and such as 

 are perforated and hyaline. It is probable, however, that while the " albocalcarefe" of Soldani 

 ^CI) belong to the former, his " margaritiferae," which he describes as iridescent, belong to 

 the type now before us. The generic designation Spirillina was originally conferred upon 

 the perforated hyahne spiral monothalams by Prof. Ehrenberg (xl a) ; but it has not 

 gained general acceptance. It was set aside by Prof Schultze (xcvii) for the term Cornu- 

 spira ; but this name was in its turn set aside by Prof Williamson (ex) in favour of 

 Ehrenberg's name, which, however, he applied to the porcellanous and arenaceous as well as 

 to Ihe hyaline forms. For the reasons already given, we think it better to appropriate Schultze's 

 generic name as the designation of the porcellanous type (^ 82), to adopt the new name 

 Trochammina for the arenaceous (^ 206), and to retain Ehrenberg's name for the type on which 

 he originally bestowed it, notwithstanding that he has since expressed his belief (' Monatsber. 

 der Akad. der Wiss. zu Berlin,' 1857, 1858) that this type really belongs not to the Foramini- 



fera but to the Polycijsti na. (See also xcix.) Examples of this type have been figured 

 by Reuss (lxxxvi) as low forms of Operculina. 



289. External Characters and Internal Structure. — The shell of Spirillina is a simple 

 undivided cylindriform tube of hyaline substance, usually perforated with rather large 

 foramina, and coiled spirally on a horizontal plane; the successive coils do not increase rapidly 

 in size, and show but little tendency to flatten themselves out, retaining for the most part 

 their circular section (ex, fig. 202). The principal variety presented by this type results from 

 the modification imparted to its surface by exogenous deposit ; for specimens not unfrequently 

 occur, in which all save the last-formed portion is studded with pearly tubercles, while the 

 foramina are so small and inconspicuous as not to be seen without close examination (ex, fig. 

 204). The diameter attained by this shell does not usually exceed l-50th of an inch. 



290. Affinities. — According to the view on which our classification of Foraminifera is leased, 

 there is no real affinity between Spirillina and either Cor)iuspira or Troclinmmina, notwith- 

 standing the precise resemblance in the forms of their shells ; since in the first of these types 

 the pseudopodia may be put forth from any part of the sarcode-body, whilst in the two latter 

 they can only be extended from the moutli of the spire. The real affinity of Spirillina is with 



