216 DR. CARPENTER'S RESEARCHES ON THE FORAMIMFERA. 



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. 1.6) ; 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 while 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 



