302 Mr. J. J. Lister. On the Dimorphism of — [Mar. 2, 
Harpe’s position afresh, that his insistence on the exceptions to the law of 
distribution in pairs was a difficulty which it would be desirable, if possible, 
to clear up. No one knew better than de la Harpe how widely the law holds 
good, and yet he insisted on exceptions. If there are strata in which only 
one form is present, how can this be reconciled with the view that both 
forms recur at short periods in the life-history of the species ? 
The difficulty appeared to be emphasised by Professor Rupert Jones’ paper 
(11) on “ Nummulites elegans and other English Nummulites,” in which he for 
the first time gave an account of the characters and distribution of the English 
species, and cleared up the confusion which had arisen over the identity of 
the type specimens of “W. elegans,” illustrated in Sowerby’s ‘ Mineral 
Conchology’ (20). 
The matter of dimorphism is dealt with very sparingly in this paper. 
It was written seven or eight years after de la Harpe had expressed 
his surprise at the apparent absence from the English beds of the forms 
named NV. Heberti and WN. Orbignyi, the -[microspheric] homologues of 
N. variolarius and N. wemmelensis var. elegans (to use the name which 
Professor Jones now applied to the species which he had previously (9) named 
NV. planulata var. Prestwichiana). 
Of the latter it is stated (on page 140) that it is one of the nummulites 
which have a large primordial or central chamber, and the megalospheric 
character is shown in figs. 4 and 8 of his Plate 9. 
The figure of the section of variolarius also shows a small megalosphere at 
the centre, and the description of this species ends with the words “according 
to Dr. de la Harpe the WV. variolarius of the Barton Beds of Stubbington and 
White Cliff Bay is the same as that of Belgium and typical. He did not find 
N. Heberti (having a small central chamber) with it, though accompanying it 
in Belgium and France.” 
Of LV. laevigatus it is said, “according to Dr. Ph. de la Harpe, the Bracklesham 
Nummulites comprise both JW. laevigatus and N. Lamarck, the latter having 
a large central chamber if 
It thus appeared to be nomeibls that “N. wemmelensis var. elegans” and 
N. variolarius, at least as they occur in our English beds, might afford some 
evidence of a similar nature to that of the supposed exceptions insisted on by 
de la Harpe; and, at any rate, so far as published descriptions went, they 
were, in the English beds, forms, to use his expression, “ privées d’une sceur.” 
I therefore spent some days last September in the Isle of Wight and on the 
adjoining coasts of Sussex and Hampshire in search of the species of nummulites 
in the Middle and Upper Eocene Beds, with the purpose of examining them 
from the point of view of dimorphism. I will now give the results. 
