216 
DR. carpenter’s RESEARCHES ON THE FORAMINIFERA. 
contiguous zones on either side, insensibly passes into the ordinary type ; and it is 
not uncommon to meet with disks, especially fossil, which exhibit in one part the 
engine-turned aspect (Plate VII. fig. 8), and in another (fig. 14) that of concentric 
zones transversely subdivided. Indeed I have sometimes found that the very same 
disk might be made to present either of these aspects, according to the manner in 
which the light is made to impinge upon it and is reflected from it. 
51. Although the rounded or ovoidal form of the superficial divisions is specially 
characteristic of the simple type of Orbitolites, yet it is by no means restricted to 
this ; being frequently met-with in the thicker disks of the more complex type, and 
being almost constant in the fossil forms that abound in the early Tertiaries. Its 
occurrence, however, may always (I believe) be considered as indicating an incom- 
plete separation between the superficial cells and the columnar cells of the inter- 
mediate stratum (^ 58.); so that the former present the shape of the latter, in place 
of the form which properly characterises them. The shape of the cell is sometimes 
marked out in unusual strength by the convexity of its lid or cover, as shown in 
Plate VII. fig. 15 ; and this feature is often so pronounced in the large fossil Orbito- 
lites of the Paris basin, as to become visible to the naked eye. A very marked 
diversity in its degree, however, as well as in the size of the cells, is to be noticed in 
the contiguous zones of another specimen (Plate VII. fig. 16) ; whence it is obvious 
that the convexity is a mere accidental variation, and is a character of no value 
whatever as regards the differentiation of species. The relation of the rounded to the 
square or oblong cells is made evident by the occurrence of intermediate links of 
transition. Thus, from such circular cells as are delineated in Plate VII. fig. 9, the 
passage is easy, through those shown in figs. 8 and 14, to those of fig. 6 (which are 
drawn under about twice the magnifying power), and thence to the square cells of 
the inner part of the portion of the disk figured in Plate VII. fig. 13. This last figure 
illustrates the important fact, that v/hile the cells in one part of the surface of the 
disk are square, others in close proximity with them may be oblong ; thus conducting 
us to the extreme form of this type, represented in Plate VII. fig. 12. 
52. The foregoing considerations seem to render it obvious, that the diversities in 
the form of the superficial cells do not afford any ground whatever for the establish- 
ment of a corresponding multiplicity of specific types, but that they must rank as 
individual variations to which there is scarcely any definite limit. If the originals of 
Plate VII. figs. 5, 7, 9, 12 and 15, had happened to have presented themselves to the 
Systematist without any of the connecting forms, he might have been pardoned for 
describing them as distinct species characterised by well-marked differences in the 
form and arrangement of their cells; but no such differentiation can be admitted in 
the face of the fact, that these are only extreme examples of variations, which show 
themselves in a minor degree between almost every two specimens brought into com- 
parison, and even between the different parts of the same disk. Moreover, when it 
is borne in mind, that the animal basis on which the calcareous skeleton is moulded 
