306 Mr. J. J. Lister. On the Dimorphism of — [Mar. 2, 
Nummulites elegans, Sow., T. R. Jones. Lbid. 
I have examined specimens from two localities, my own from Alum Bay 
anda sample from Huntingbridge. The two sets are somewhat different, and 
it will be convenient to deal with them separately. 
Those from Alum Bay (Plate 5, m) are from the bed which is regarded by 
geologists as the bottom layer of the Barton Clay, passing conformably into 
the underlying Bracklesham Beds (and often referred to as Bed 29 of 
Prestwich’s section). They are apparently identical with the specimens on 
the tablets 44,007 (1) and (2) of the Sowerby Collection now in the British 
Museum. 
On grinding down 95 specimens to display the initial chambers, I find 93 
to be megalospheric, and 2 to be microspheric, a proportion of 46°5 to 1. 
In the megalospheric specimens (the N. wemmelensis de la Harpe and van 
den Broeck, var. elegans, Sow.) M varies (fig. 1) from 66 to 148 yp, the average 
being about 96 yw (Plate 5, a—-a”). 
The largest specimens of this form are about 3 mm. in the longer diameter 
of the test. 
In the two microspheric specimens the value of m is 17 and 19 w. The 
diameter of the test in these specimens does not exceed that of the larger 
megalospheric forms.* 
The Huntingbridge specimens which I have examined were contained in 
the collection of the Sedgwick Museum at Cambridge and were kindly placed 
at my disposal by Professor Hughes. They were obtained by Mr. H. Keeping 
from this locality, which is near Fritham in the New Forest.f 
On comparing these specimens with those of Alum Bay certain differences 
* On looking closely at tablet 44,007 (1) in the Sowerby Collection in the British 
Museum, in which three specimens are represented in section, it will be found that one 
of them (that immediately above the yellow label) is different from the others, and with 
the assistance of a low power of the microscope it becomes clear that this is a section of 
a specimen of the microspheric form. It is in fact an example of the WV. Orbignyr 
(Galeotti), the apparent absence of which from the English Beds occasioned de la Harpe’s 
surprise. 
+ In his paper (4) on the Bracklesham Beds of the Isle of Wight Basin, Mr. Fisher 
says, p. 80, of the beds a few feet lower in the series, “the character of the matrix at 
Huntingbridge approaches more nearly to some of the Barton deposits than to any 
of the Bracklesham strata.” This was written before Mr. Keeping found the nummulite 
bed in question, and it would appear that the presence of this characteristic fossil of 
the lowest Barton bed confirms the suspicion which seems to have been in Mr. Fisher’s 
mind that he was here approaching the upper limit of the Bracklesham series. 
The position of the locality is clearly indicated by the reference in Mr. Fisher's 
paper to the Ordnance Map. On a recent visit to the Forest, I failed to find any one who 
recognised it by the name of Huntingbridge, and an old keeper told me that it is 
now known as Three Bridges. 
