240 FAMILY NUMMULINIDA. 



in Orbitoides we have the discoidal plane of cyclically arranged chamberlets, overgrown on 

 either side with piles of flattened secondary chamberlets, which on the one hand bear a strong 

 resemblance to those of Tinoporus, and on the other are analogous to those formed by the 

 subdivision of the alar lobes in certain Nummul'mce. In regard to complexity of structure, 

 Nummulina and Orbitoides may be considered as holding a corresponding rank ; and it is very 

 interesting to remark that these two types attained their highest development at the 

 same geological periods, and that they represented each other in different localities. 

 Owing to the metamorphic condition of the shell of FusuHua, a type which is only known 

 as occurring in the Palseozoic series, it is not certain whether it is to be rightly referred to 

 this family, or should be placed in the porcellanous group in close proximity to Alveolina, 

 which it resembles in its plan of growth ; and the only reason I can advance for regarding it 

 as an early and somewhat rude representative of the Nummuline type, is afforded by faint 

 indications of a tubular structure in its shell, and by an appearance of duplication in its 

 septal lamella. 



418. According to the system of M. D'Orbigny, the genera which we group together in 

 this family would be distributed under three of his orders, as follows : 



Order II. — Cyclostegues. Cycloclypeus, Orbitoides. 



Order IV. — HELicosxiiGUES. Fusulina, Nummulina, Operculina, Polystomella 

 (including Nonionina). 



Order V. — Entomostegues. Amphistegina, Heterostegina. 



In our view their affinities may be represented somewhat as follows: 



FAMILY NUMMULINIDA. 



Amphistegina. 



Polystomella Nummulina 



Nonionina Operculina . 



Fusulina ? Heterostegina . Cycloclypeus . Orbitoides- 



Alike by Amphistegina and by Polystomella this family is connected with the genus 

 Eotalia ; whilst by some of its most degraded Nonionine forms Polystomella is related to 

 Pulvinulina. The relation of Heterostegina to Orhivulina, and of Cycloclypeus and Orbitoides to 

 Orbitolites, is one of analogy only, arising from the similarity of their respective modes of 

 growth, and is no more indicative of any real affinity than is that which arises out of the 

 superficial resemblance between Peneroplis and Operculina, two types which are separated 

 from each other in every character of real importance as widely as any two polythalamous 

 Foraminifera can be. 



