Nomenclature of the Foraminifera. 233 



alar flaps and become Operculina. In the one case we have 

 Nummulina with thin edges; in the other, Nummulinee with thin 

 centres. The difi"erence in the width of the whorl, itself also a 

 variable condition, is the chief feature distinguishing OpercuUna 

 from Assilina. 



Taking, however, the pattern of the alar growth of the seg- 

 ments as a feature of some value, we are further puzzled by 

 finding the simple "radiate" plan combined in some NummuliruB 

 with a sinuous outline of the alae, or passing so gradually into 

 the " sinuate " plan that the distinction does not imply a dif- 

 ference. The same may be said of the relation of the " sinuates " 

 to the " reticulates," although the gradation is not so common. 

 The N. complanata of Dax, however, shows occasionally inoscu- 

 lations of the alar septa sufficient to support this statement. 



We cannot accept the granulated condition of the surface as a 

 specific character. It arises primarily from an increase of shell- 

 matter either along the septa or on the points where the alar 

 septa cross each other, and is concomitant with a good condition 

 and stout growth of the shell. It is not limited, however, to the 

 septa, but occurs in the interspaces of thin shell. 



Still less can we take as an essential character the relatively 

 large size of the primordial chamber. There is reason to sus- 

 pect that certain Foraminifers commencing with a large chamber 

 and growing more or less freely, but not attaining a large size, 

 are varieties, or, rather, free-gi-owing individuals soon arriving 

 at their limit of growth. This holds good among Xummulina. 

 With few exceptions, all the specimens under 12 millimetres in 

 diameter that are figured in section in D'Archiac and Haime's 

 Monograph have a large primordial chamber ; for instance, N". 

 Garanensis, N. Molli, N. Lamarcki, N. latispira, N. Tchihat- 

 cheffi, N. Meneghinii, N. striata, N. Vasca, N. Rouauiti, N. curvi- 

 spira, N. contorta, N. variolaria, N. Lucasana, and N. Guettardi. 

 The other small forms are N. intermedia, N. Fichteli, N. Lei/meriei, 

 N. mamillata, X. Beaumonti, N. discorbina, X. Heberti, X. macella, 

 and jY. Ramondi, in which the evidence of a large central chamber 

 is wanting. None of these can we regard as worthy of specific 

 rank, either for the reason above stated, or because they can 

 easily fall into the suite of one or other of the thirty-two remain- 

 ing ; for we cannot accept as specific distinctions the differences 

 in the proportions of chambers and whorls, diameters and thick- 

 ness, which have been so strongly urged by other observers. 



Of the simply radiate Nuramulines, the simplest and perhaps 

 the oldest-known is the X. radiata, Fichtel and Moll ; but these 

 forms are lost in the next grade, the sinuo-radiate. 



Among the radiate and sinuo-radiate there are three that well 

 represent the group — X. planulata, X. Viquesneli, and X. Bia- 



