KONGL. SV. VET. AKADEMIENS HAXULINGAR. BAND 



25. n:o 9. 9 



Fig. 35— .36 Nod. communis d'Okb. ap])roacliiiig the slender form called badenen- 

 sis d'Orb. 



Thus, amongst the whole assemblage of tigured forms which v. Reuss has distin- 

 guished as 19 species, we are unable to discern more than one type species with its 2 or 3 

 varieties. Many more instances of a thoroughly arbitrary differentiation of forms could 

 be produced, and the chosen one is not to be considered as being of a moi'e extravagant 

 character than that displayed in works of several other writers. 



Amongst features and morphological structures which cannot reasonabl}' be con- 

 sidered as of any but relative value for distinctive purposes are to be pointed out the 

 following : 



the absence or presence of a marginal iving or keel, oi marginal spines, o^ psetidopodal 



tubes, of "beads' scattered over or covering the surface, and of limhation of the 



sutures. 



Striation of the shell-surface is also a rather unsteady feature, one part of the shell 

 often being striated, another part smooth. 



The number of ridges is subject to great variation, for instance among the Lagenfe, 

 Nodosarinai, and Miliolina\ 



The shape of the aperture of some genera exhibits a remarkable degree of variation, 

 with great di\'ersity between the young and older stages in one and the same "colony", 

 particularly amongst Miliolina^. 



The limitation of the genera in this class has been subject to just as many incongruities 

 as the ranging of the species. Several families, particularly Nodosarina?, Bulimina^, Miliolina?, 

 offer ample illustrations of the shortcoming of an uncalled for endeavour to dissociate 

 allied types. When the, boundary-lines of distinction drawn up between the genera at 

 every instance not hold good, we must fall in with a spurious differentiation encumbering 

 the system with distinctions totally in want of reasonable qualifications. The usual result 

 of such a device is that the student soon will be confronted with forms which reasonably 

 would be ranked under one species, but still, according to the artificial differentiation, 

 are disjoined under two — three spurious genera. Such instances are not seldom met 

 with in d'Orbigny's and other distinguished authoi-s' arrangement of genera. In the 

 agglutinating groups the institution of genera seems founded on a singularly arbitrarious 

 basis. Nay, the whole order "arenaceous' is scarcely based on sound discrimination. 



The inconsistency in instituting the "arenaceous" Foraminifera as a separate group 

 is shown among such genera as Textularia, Miliolina and BuUmina, which often exhibit 

 forms with agglutinating test, and still must be ranged with their calcareous congeners. 

 Certain facts seem also to support the view advanced by Melch. Neujiayr' and others, 

 that a great deal of the homogeneous calcareous Foraminifera have taken their origin from 

 arenaceous forms. It ^vould, therefore, not be surprising to meet with Polystomella?' 

 NonionintB, and other calcareous forms, in the same agglutinating condition. Further in- 



' M. Neumayr: Die iinlui-liclien Vfrwiuultschiiftverhaltnisse der sclialentragenden Foriiiiiiiiifereii ; VVicii, 

 Ak. Sitz. Ber. (1887), 95, I. 



K. Sv. Vet. Akad. Handl. Bond 25. N:o 9. 2 



