202 t)R. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



or between the thickness of different parts of the same specimen, and the distance of 

 these parts from its centre. The only remarkable departure from the ordinary form 

 which I have met with, presents itself in certain Orbitolites from the Feejee Islands, 

 of which several specimens in the Museum of the Royal College of Surgeons, and 

 two in my own possession, exhibit a curious plication towards their margins ; the 

 degree of this departure varies so much, however, in different individuals, the plica- 

 tion being almost obsolete in some (see Plate V. figs. 2, 3), that it cannot be admit- 

 ted to mark a specific diversity; and considering that these disks always grow on 

 the surfaces of other bodies, it can scarcely, I think, be considered improbable, that 

 the plications originate in the inflections of those surfaces*. These same specimens, 

 moreover, also exhibit another curious abnormality ; namely, the projection of the 

 upper and lower edges of the margin, so that a groove is left between them, the pro- 

 jecting laminse being thin and foliaceous, and their cells very irregularly arranged. 

 This peculiarity, again, being far from uniform in its degree, and being altogether 

 wanting in specimens which in other respects precisely resemble those with plicated 

 and foliated margins, must be considered merely in the light of an accidental variety ; 

 but I cannot suggest any explanation of its occurrence, or of its limitation (so far as 

 I am aware) to this particular locality. 



26. The surface of the disk (Plate V. fig. 6) is marked out, as in the simpler 

 type, by concentric zones of cells, the number of which bears a general (though not 

 a constant) ratio to its diameter ; these cells are usually somewhat rectangular in 

 shape and sometimes approach a square, but are more commonly nearly twice as 

 long in the line of the radius of the disk as they are in the transverse direction, their 

 long sides being parallel to each other. We shall hereafter see, however, that the 

 form of the superficial cells is very subject to variation, and that it may be very 

 dissimilar even in different zones of the same disk (^[ 48-52). The pores at the 

 margin of the disk are disposed, as in the simpler type, between the projections 

 formed by the convexities of the cells ; and each is usually surrounded by the pro- 

 jecting annulus formerly noticed (^[ 19). The disposition of these pores, however, is 

 far from regular, as they seldom form rows that seem exactly continuous with each 

 other, either horizontally or vertically ; and the number of pores in each vertical 

 row is by no means constant, even in different parts of the margin of the same 

 disk-f". 



* I have elsewhere noticed the fact, that various species of Orbitoides are disposed to exhibit a like con- 

 tortion ; and that the well-marked ephippial shape which some specimens present, is nothing else than an acci- 

 dental variety (see Quart. Journ. of Geol. Soc., vol. vi. pp. 34, 35). 



t In following the description of the internal structure of this type of Orbitolite, it will be convenient for 

 the reader to make frequent reference to the ideal representation which has been built up in Plate V. fig. 6, 

 by the combination of materials furnished by a great number of preparations which are represented in separate 

 figures accompanying the original Memoir in the Archives of the Royal Society ; these last of course furnish 

 the real authority for every point in the description, the ideal figure, however, serving to display the relation 

 of different parts to each other in a manner that no single preparation would possibly admit. 



