472 Messrs. W. K. Parker and T. R. Jones on the 



of the specimen figured by Lamarck has escaped the critical in- 

 vestigation of the many writers on Foraminifera. It was only 

 when we met with an individual (and that unique) in the rich 

 collection of Tertiary shell-sands belonging to Sir C. Lyell that 

 we found that this suborbicular shell, well characterized by La- 

 marck's figure, was an almost cyclical variety of Vertebralina. 

 Accustomed as we are to the elongate, articulate, and crozier-like 

 forms of Vertebralina (including Articulina), it is difficult, with- 

 out having a wide experience of their varieties, to recognize the 

 true relations of the form under notice. In one direction, Ver- 

 tebralina is modified, in its weaker growths, by a disposition to 

 exhibit simple rectilinear forms, with out-drawn equal-sized 

 chambers, giving a rod-like shape. In this case the primordial 

 chamber is long and tube-like, a rare feature in Foramini- 

 fera. The next step is taken by the primordial chamber being 

 subglobular, the second chamber being laid on it as a semilune, 

 and followed by rectilinear chambers. In further gradations 

 more and more chambers are arranged spirally (two, three, or 

 four completing the whorl) around the first chamber, before the 

 Articuline growth commences, whether this latter assumes the 

 rod-like or the Vertebraline condition. Arrests of development 

 at the spiral condition are not uncommon in any of these forms : 

 thus we have among others the broad Vertebralina Cassis } D'Orb. 

 For. Cuba, pi. 7. f. 14, 15. 



The growth of a linear succession of chambers from the spiral 

 base is the normal habit of Vertebralina, the anterior end of each 

 chamber usually presenting an elegantly curved outline, with a 

 somewhat outspread or recurved margin. In this dimorphous 

 condition we have usually from two to five of these forth-grow- 

 ing chambers, which are either subcylindrical, more or less de- 

 pressed, or broadly flattened, and either longer than broad, sub- 

 quadrate, or transversely oblong. .It is the extreme opening- 

 out, or transverse extension, of these wider and short chambers 

 that leads us to the lateral outgrowing and overlap of the very 

 narrow and transversely elongate chambers in Renulites opercu- 

 laria y , which, by the successively increasing length of its sym- 

 metrical, concentric, linear chambers, with their incurved ends 

 turned towards the spire, and overlapping the edges of the older 

 chambers, attains this very rare subcyclical form, flat, kidney- 

 shaped, and resembling the operculum of some minute Gas- 

 teropod. 



Vertebralina is one of the Ayathistegia, white, opake, and 

 non-tubuliferous. It is nearly allied to Miliola on one hand, 

 and to Cornuspira on the other. In the specimens under notice, 

 simple as is the form of the typical shell (V. striata, D'Orb.), we 

 have indications of an affinity to the cycloidal Orbiculina and 



