122 



that the septa thus dividing each segment into smaller compart- 

 ments are little more than strong calcareous pillars. The segments 

 are closed in above and below by the thin, shelly layers, 17, d, which 

 are perforated by remarkably large pseudopodian foramina, and 

 which have obviously answered the same end as the canals (fig. 

 12, c). 



On making a horizontal section of a similar example a little below 

 the level of the surface, we obtain the result delineated in fig. 18, in 

 which portions of three concentric circles are shown. 18, a, a, are 

 the septa, separating contiguous segments, and correspond with 17, a, 

 in the vertical section. 18, b, are the segments or vertical cells, if 

 such they can here be called. 18, c, are open canals or orifices, corre- 

 sponding with 17, b, and maintaining a communication between adjoin- 

 ing circles of cells. The analogous apertures, 18, d, correspond with 

 the large passages, 17, d, and communicate laterally between the 

 different subdivisions of the same circle. The vertical septa (17, a, 

 and 18, a) are the most uniform in their contour ; those which unite 

 them together (17, e, and 18,/) having, as already observed, the cha- 

 racter of thick, transversely- arranged pillars. 



At 18, e, a portion of the external shell is visible, exhibiting the 

 true pseudopodian apertures, which are larger in this species than in 

 any other Foraminifer with which I am acquainted : we also see 

 from this portion of the specimen, in which the section is ground 

 very thin and close to the external shell, that whilst no foramina 

 exist along the line of the concentric septa (18, a'), they are abun- 

 dant opposite to the lines of transverse pillars (18,/), showing that 

 the latter do not come in contact with the external shell, but always 

 leave an open space between the two, which admits of a correspond- 

 ing extension of the soft animal in immediate contact with the fora- 

 minated portion of the parietes. This is seen at 18, e, where, owing 

 to the thinness of the section, these transverse pillars have been 

 ground away. 



On comparing the structures thus revealed to us with those existing 

 in O. complanata and its Tongese ally, we cannot but be struck with 

 their close resemblance to each other. The construction of the septa, 

 the arrangement of the segments, and the distribution of the intra- 

 septal canals, are as similar in the three cases as is compatible with 

 the primary differences in their external forms. In the case of the 

 intraseptal canals, the principal difference appears to be in their 

 relative numbers. In O. complanata (fig. 9, 6 and c) we have but 

 one series of orifices arranged in the median plane. In the Tongese 



