250 Mr. II. J. Carter on the Structure of the larger Foraminifcra. 



test respectively, — the last three, four, or more, being of succes- 

 sive sizes up to the last of all, which is least developed. 



The same principle obtains iu the formation of the test and 

 propagation of Orhitoides dispansa and Orbitolites Mantelli, Cart. 

 [Orbitoides Mantelli, D^Orb.) ; but the canal-system is different, 

 and there are no columns of condensed shell-substance in the 

 latter. In Orbitoides dispansa each chamber is united to the two 

 in fi'ont and the two behind it by stolon-processes, as in Cyclo- 

 chjpeus, Carp.; and there is an annular canal behind each row, 

 which is united, by straight, transverse, interseptal or inter- 

 cameral branches, with that in front and behind it in each half 

 of the test. The latter system also exists in Orbitolites Man- 

 telli', but the stolon-processes are represented by oblique canals 

 which radiate from the centre to the circumference, and here in 

 this manner also unite each chamber with the two in front and 

 two behind it ; while, as the chamber becomes vertically elon- 

 gated towards the circumference, the oblique canals are increased 

 to two, four, and six in number in the outer rows, one above 

 another, so as to resemble their disposition in Orbitolites, as 

 shown by Dr. Carpenter^s diagram. In the annular canals we 

 cannot help seeing the analogues of the great spiral canals in 

 Operculina and Nummulites Ramondi, &c., if not in all Nummu- 

 lites; while in the stolon-processes of Orbitoides dispansa and 

 the oblique canals of Orbitolites Mantelli and Orbitolites com- 

 planata, we seem to have a combination of the marginal plexus 

 and interseptal canals; for they both open ultimately at the 

 margin or circumference of the tests respectively. The columnar 

 chamber-structure, on the other hand, in both, which corresponds 

 with the vertical development of Nummulites (that is, the exten- 

 sion of the chambers to the umbilicus on each side the horizontal 

 plane), has its parts united by ascending and horizontal stolon- 

 processes, which indirectly give existence to the propagative 

 spherules throughout, for the same kind of spherules ai-e deve- 

 loped both in the chambers of the horizontal plane and in the 

 columnar chambers, even to the very centre of these fossils, as 

 in Nummulites and Operculina. 



The tests of Conulites (n. gen.) and Orbitolina lenticularis are 

 developed upon the same principle as the rest, and both present the 

 same kind of propagative spherules in the chambers. Conulites, 

 however, has the same columnar chamber-structure and columns 

 of opake shell-substance as Orbitoides dispansa, but with a helical 

 layer of chambers externally, something like the horizontal layer 

 of Nummulites ; while Orbitolina lenticularis has no columns of 

 opake matter in its columnar chamber-structure, and has a cyclical 

 arrangement of the rows of chambers externally, like Oi-bitoides 

 dispansa, Orbitolites Mantelli, and Oi-bitolites complanata. 



