68 Miscellaneous. 
species must be regarded as the most perfect geometrical type of 
inrolment in five directions. In the Pentelline, as in the Quinque- 
loculine, it is observed that the forms A and B are less dissimilar 
in appearance than in the other genera. Nevertheless these two 
forms are distinguished at once by the difference of size that occurs 
in their first chambers. Moreover, around the central chamber of 
the form B we recognize the presence of some small chambers ; but 
starting from this point the succeeding chambers acquire the Quin- 
queloculine arrangement so characteristic and so constant in the 
form A. 
Fabularia discolithes, Defr.—The individuals of the form A are 
always exceedingly small; the largest have as the maximum not 
more than seven embracing chambers arranged alternately on each 
side of the central chamber, which measures 270 px. The first serial 
chamber, which represents the canal of the Biloculine, remains 
simple, while the succeeding ones are divided by longitudinal par- 
titions into narrow more or less circular chambers which communi- 
cate with each other by lateral canals. The inrolment, like that of 
the Biloculine, takes place in accordance with a single plane of 
symmetry. 
Kabularia discolithes, Defr.—A transverse section of the form B 
shows that the chambers present three principal modifications in 
their arrangement :— 
il Around the central chamber, which measures 21 p, there are 
grouped five simple chambers ; then the nine succeeding ones are 
arranged more or less irregularly in accordance with their directions. 
The last two are divided by a thick longitudinal partition, which 
cuts them into two. 
. From this point the new chambers are regularly opposite to 
each other; the first six or seven of this series present numerous 
longitudinal canals arranged in a single series. 
3. Lastly, in the third phase the last chambers, to the number of 
twenty or twenty-two, present a series of more or less irregular 
supplementary canals towards their inner part. 
From this very brief investigation it appears that all the species 
of Miliolites that we have studied are dimorphous. One may easily 
recognize this dimorphism by comparing numerous sections; the 
form B will always be distinguished by a much smaller central 
chamber surrounded by a greater number of chambers than in the 
corresponding form A. 
In the presect state of our knowledge it is difficult to pronounce 
a definite opinion upon the cause of this dimorphism ; nevertheless 
it seems to us that there are only two possible hypotheses. 
In the first place it may be supposed that each species is repre- 
sented by two forms distinct from their origin. But hitherto we 
have been unable to discover in any of the numerous species that 
we have studied very young individuals of the form B. 
The second hypothesis consists in assuming that the dimorphism 
is the result of a final evolution. Every individual would then pass 
