304 Mr. J. J. Lister. On the Dimorphism of — [Mar. 2, 
Examination of them by section, however, yielded the following results :— 
Nummulites variolarius (Lamk.) (WV. Heberti, d’Arch.). 
Among 168 specimens examined in section 163 are megalospheric, and 
5 microspheric, a proportion of 33 te 1. 
In the megalospheric specimens (Plate 4, a, a’, a’’) the mean between the 
longest and shortest diameters of the initial chamber, as it appears in 
the section* varies, as shown in fig.1, from 38 to 102 pw, the average size 
being about 68 w. The largest specimen of this form is 2 mm. in the longer 
diameter of the test, the average diameter in 13 large specimens is 1°8 mm. 
In the mzcrospherce form (the NV. Heberti of d’Archiac)t the mean diameter 
of the initial chamber (= m) in the five cases is 15, 16, 16, 16, and 17 p 
(Plate 4, 6 0’). Specimens of this form also attain a diameter of 2 mm., and the 
average in five large specimens is 1°92. There is thus a slight tendency in 
this species for the microspheric form to exceed the megalospheric in size. 
(See also the table on p. 311.) 
Nummulites Orbignyt (Galeotti), (wenmelensis, de la Harpe and van den 
Broeck), var. elegans, Sow.} 
Operculina Orbignyt, Galeotti, ‘Mem. couronné. Acad. de Belgique,’ T. 13, 
p. 54, 
* T use d/ to indicate this mean value in the megalospheric form, and m in the 
microspheric form. 
+ In the ‘ Bull. Soc. Géol. de France,’ 1881, p. 172, de la Harpe says ‘“ Enfin pour le 
NV. variolaria, Sow. : le fait est plus frappant encore ; on est presque toujours obligé de 
briser ces petites nummulites de Paris, Bruxelles, Gand, Stubbington et Isle de Wight 
pour savoir si, oui ou non, elles ont une chambre centrale, et si l’on doit les ranger parmi 
les V. Heberti ou variolaria.” 
{ Perhaps it is due to my readers to set before them as briefly as possible some of the 
changes of nomenclature of which this pretty little nummulite has been the victim. 
In the ‘ Mineral Conchology,’ vol. 6 (1829), p. 76, Sowerby set about describing three 
species of nummulites, figuring them on Plate 538. The groups of figures in illustration 
of each species are numbered 1, 2 and 3, though the group numbered 3 comes in the 
middle and that numbered 2 below. The several figures in each group are not numbered, 
but by counting the figures and following the order of the numbers of the groups, a 
number may be given to each figure. In this way the numbers 6 to 11 may be assigned 
to the figures in group 2, the lowest on the Plate. 
The first and third species enumerated are J. laevigata and J. variolaria, and about 
their identity there is no question; but unfortunately Sowerby confused two distinct 
species under the name J. elegans, constituting his second species. The two species thus 
confused appear to have been, as shown by comparing the figures with the specimens in 
the Sowerby Collection now in the British Museum :— 
N. wemmelensis var. elegans (called N. Orbignyi var. eleguns in this paper), mounted on 
tablets 44,007 (1 and 2), and WN. planulata (Lamk.), said to come from Emsworth, and 
mounted on tablets 44,007 (38 to 5). 
