16 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



ferous beds, which is arenaceous, smooth, or only slightly rough as to its surface, and nor- 

 mally imperforate. In the Permian magnesian limestones this is largely replaced by the 

 true Nodosarian type, but in its simplest modifications. A few lingering specimens of the 

 older form still recur up to the Middle Permian beds, but except for their larger size and 

 somewhat thicker tests, they are scarcely distinguishable from their hyaline isomorphs. 

 In deposits of later age we have two distinct and well-defined series, the one normally 

 much more arenaceous, the other much more hyaline, than their Carboniferous prototype. 

 Direct evidence of continuity cannot be adduced in such a case ; but, if we accept its 

 possibility, it is not unreasonable to suppose that these early quasi-Nodosarians are the 

 precursors, not to say the lineal ancestors, of two still living, and now widely separated, 

 groups of Foraminifera. 



It is not needful to press this argument by pursuing it through other Carboniferous 

 genera and their more recent isomorphs ; to do so successfully would require more know- 

 ledge than at present exists as to the relative age of Carboniferous beds widely separated 

 geographically ; but any one familiar with the various modifications of the Rotaline genera 

 will not fail to be struck with the possibility of their common ancestry in the genus 

 Endothyra. 



Turning to the PERFORATA, we must be prepared for very different conditions of dis- 

 tribution, the contrast being possibly greater in the number of individuals (if we except 

 the genus Fiisulina) than in the number of species represented. Thus, in the family 

 LAGENIDA the list embraces but three very rare and somewhat obscure Carboniferous 

 forms of Layenee and a few simplePermianTVWosanW. The second family, GLOBIGERINIDA, 

 has its principal development in the genus Textidaria, the larger, rough varieties of which 

 are common in the Carboniferous, the small, delicate, ambiguous examples being found 

 very locally distributed in the Permian rocks. It is worth remembering that Textularia 

 is almost as difficult a genus to place satisfactorily in any natural classification as 

 Valvulina. Its best and most characteristic type, T. agylutinans, is as rough and sandy 

 as Lituola itself, and frequently as labyrinthic in its internal structure ; and between this 

 and the transparent, delicate, perforate forms, the genus shows every gradation of texture. 

 But in Textularia the thin-shelled, porous varieties constitute the larger part of the genus, 

 whilst in Valvulina the reverse is the case. Were it determined to establish an inter- 

 mediate sub-order for the reception of the variable genera at present classed with 

 the LITUOLIDA, a course that would relieve the existing classification of many anomalies, 

 Textularia would find its natural place in company with Endothyra and Valvulina, the 

 common types of the Carboniferous age, with Involulina of the Lias, Verneuilina and 

 jBulimina (Ataxophragmium) of the Chalk, and some other similar generic and quasi- 

 generic groups. 



Besides Textularia, the only representatives of the GLOBIGEUINIDA in the Carboniferous 

 fauna are very rare examples of three Rotaline genera, Planorbulina, Pulvinitlina, and 

 Calcarina, and their distribution is exceedingly limited, being confined to one or at most 



