68 .FAMILY MILIOLIDA. 



Genus II. — Cornuspira (Plate V, fig. 16). 



82. Hisfori/. — The genus Cornuspira was instituted by Prof. Schultze (xcvn, p. 40), for 

 those calcareous-shelled Foraminifera which form a flat spire like that of a Planorbis, and 

 have their cavity simple and undivided ; and two species were distinguished by him, one 

 of them, C. planorbis, having the shell solid, the other, C. perforata, having it finely 

 porous. Prof. Williamson (ex, p. 91), whilst recognising both these forms, and describing 

 another in which the shell is arenaceous, reverted to the generic name Spiri/Ii/ia, which 

 had been previously given by Ehrenberg to a shell resembling Schultze's C. perforata, 

 and included all three forms under that designation ; at the same time changing the 

 specific name of Schultze's C. planorbis to adopt that of foliacea, which had been pre- 

 viously bestowed by Philippi upon a more advanced form of the same organism. Soldani 

 (by whom this shell seems to have been first figured), Philippi, Williamson, and Messrs. Parker 

 and Rupert Jones, have all recognised in its opaque-white porcellanous character a close 

 resemblance to that of the MilioUnce. This resemblance is unquestionable ; and if there be any 

 truth in the principles enunciated in the two preceding chapters, it is obvious that the imper- 

 forate porcellanous spirals and the perforated hyaline spirals must be regarded, in spite of 

 their almost exact resemblance in external form, as belonging to two fundamentally different 

 types. Reserving, therefore, the name Spirillina as the generic designation of the latter, I 

 concur with Messrs. Parker and Rupert Jones in thinking it expedient to make use of the 

 name Cornuspira as the distinctive appellation of the former. 



83. External Characters. — The shell of Cornuspira is a simple flat spire, the suc- 

 cessive turns of which at first increase but slowly in width, but which at last opens 

 out rather suddenly, like that of many other Foraminifera growing upon the same type 

 (Plate V, fig. 16). The successive convolutions are in contact at their edges, but the later 

 do not extend themselves over the earlier, so that the whole of the spire remains visible 

 externally on each lateral surface. Not the least appearance of septal bands or constric- 

 tions presents itself at any part of the spire ; except that a slight depression may some- 

 times be detected, which marks ofl^ the primordial chamber from the spire that proceeds from 

 it. In the young form of this shell the tube is cylindrical or nearly so, and its aperture is 

 round ; but as it advances in age and flattens itself out, whilst the spire undergoes a rapid 

 increase in width, its two surfaces become so closely approximated that the form of the 

 aperture changes from a circle to a long, straight-sided fissure (fig. 1 6, a). The compressed 

 whorls of the adult often show a series of irregularly alternating ridges and depressions, 

 which cross the course of the convolutions with a convexity directed forwards, and these 

 seem to mark the successive additions which the shell has received. Occasionally, as in many 

 higher types, an abrupt narrowing of the spire takes place, so that the convolution is con- 

 tinued on the smaller scale of some previous portion of the whorl, as is shown in fig. 16. 



84. Internal Structure. — The entire absence of septal divisions, indicated by the external 

 aspect of this type, is proved by an examination of its internal structure, which shows that 

 the cavity occupied by the sarcode-body of the animal is perfectly uninterrupted, except 



