Hrron-Ali,kn and Karlano — Stiidij of Vcrnetdlina pohjstrophn. loO 



degeneration, rather than as representatives of Poneroplis, because of the 

 existence of the intermediate forms just alluded to, in which the subdivision 

 dies out in the terminal chambers, and also because they agree so closely in 

 external features with small examples of typical Orbiculina that they cannot 

 be distinguished from them by the external characters of the tests." 



Lister compares these specimens with Schlumberger's figure of Archiacina 

 munieri, and suggests the identity of Schlumberger's form." This seems 

 highly probable, and it is not the only instance in which Schlumberger has 

 obscured knowledge by the erection of fictitious barriers. Tlie difficulties 

 attached to an explanation of the abnormal variations are increased, and not 

 diminished,, by the removal of the specimens to another sub-genus. 



Our own experience of this interesting form of variation differs from 

 Lister's, inasmucli as we have not hitherto observed any specimens such as 

 he describes, in which an individual, having started growth with an 

 "orbiculine" shell, subdivided into chamberlets, subsequently degenerates 

 into the peueropline form, with individual chambers. All the specimens we 

 have examined (and they are very many) have proved to be constant in one or 

 other form ab initio, and a series of mounts of baby shells in balsam contirms 

 this view. Subdivision into chamberlets either occurs from the very begin- 

 ning (tig. 1), following the primordial chambers, or is entirely wanting. 

 Moreover, although no peaeropline specimen which we have seen attains 

 any large size as compared with the comparatively huge dimensions some- 

 times attained by Orbiculina, the specimens can hardly be described as 

 ".stunted," for they differ little as regards external form and condition from 

 typical Orbiculina of the same size, abundant in the same gatherings. 



These peneropline variations are, however, few in number as compared 

 with the typical shell. A noticeable feature, when the tests are examined 

 in balsam, is the marked thickening of the septal face of the shell (fig. 2), 

 so that the concentric septa become enormously thick as compared with 

 typical Orbiculina. Thus the strength and rigidity lost by the suppression 

 of the secondary septa are to a great extent recovered. 



We have already referred to Orbiculina as presenting a remarkable 

 resemblance to our genus Cycloloculina.'* The resemblance is entirely super- 

 ficial so far as the typical Orbiculina is concerned ; but in these degenerate 

 varieties the undivided chambers raise the resemblance to a point approaching 

 true isomorphism. 



'' 0. Sulilumberger : '" Notes .suv iiuolques Foraininiferes .... tin (iolfe ilo Gascogne." 

 Fuuille des Jeuues N.iturali.stes, 1883, No. 153, j). '22, PI. iii, figs. 2, 2". 



'* K. Heron- Allen and A. Earlaud : " On Cycloloculina : a new Generic Type of the 

 Foramiuifora " .1. R. Micr. Soc, 190S, p. 536. 



