214 
DR. CARPENTER’S RESEARCHES ON THE FORAMINIFERA. 
to exist in regard to superficial area ; and which also proves that the relative thick- 
ness of the central and of the peripheral portions is equally liable to variation, 
46. It seems obvious, from the foregoing considerations, that neither the absolute 
nor the relative dimensions of the individual parts of these composite fabrics, can, 
any more than the dimensions of the entire disks, be taken as affording valid charac- 
ters for the discrimination of species; and that such a wide range of variation exists 
among individuals, as would, if the extreme cases alone were known, seem fully 
to justify their separation under distinct specific designations. Thus, if the two 
extreme forms, figs. 1 and 4 (Plate VII.), had been the sole objects of comparison, 
most naturalists would undoubtedly have considered the strongly-marked difference 
in the size of their respective nuclei to entitle them to rank as separate species; and 
even if fig. 2 or fig. 3 had been brought into comparison with them, it might have 
been a question whether it should be associated with fig. 1 or with fig. 4, or should 
rank as a third species intermediate between them, or should be considered as a con- 
necting link specifically identical with both, and therefore establishing their specific 
identity with each other. The comparison of the entire series must be felt to remove 
all ground for hesitation on this point, since it is manifestly impossible to draw a line 
across any part of it, which should divide it into two or any larger number of groups, 
respectively characterized by constant and well-marked differences in size. And 
here again, therefore, we have evidence of the great importance of bringing into 
comparison a sufficiently large number of forms, to enable us to determine in some 
degree the measure of individual variation. 
47. Variations in Shape. — The very strong tendency which we have seen to pre- 
vail in the Orbitolite, not only to the maintenance of the circular type in the regular 
growth of the disk, but to its reproduction after accidental injuries, seems to prevent 
the occurrence of any considerable variation in its general form, except such as may 
be directly produced by external agencies. The circular sometimes gives place to an 
elliptical shape (Plate VII. fig. 4), especially in young specimens, whose form is more 
determined by that of the nucleus than is that of older individuals. And the occur- 
rence of such a variety in the recent type, makes me indisposed to admit that ellip- 
ticity of shape can be in itself a sufficient basis for the specific differentiation of any 
fossil form of this genus. Of the marked differences in the general aspect of the 
disks, which may arise from differences in the relative proportions between their 
thickness and their diameter, and in the relative thickness of their central and 
peripheral portions, mention has been already made (^^ 17 and 32.). And the 
only other important departure from the typical shape which I have met with, either 
in the simple or in the more complex form, has been described under a former 
head (^ 25.). 
48. Variations in the Form of the Superficial Cells, and in the Markings of the Sur- 
face. — The appearances presented on minute observation by the surface of the Orbi- 
tolite, are so far from being uniform, that to any one whose eye had not become 
