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On two gigantic Types of Foraminifera. 



[Apr. 22, 



rally at right angles to the septa or nearly so, but are otherwise irregular 

 in their arrangement. No large primordial chamber, such as is common 

 among Foraminifera, has been yet discovered in Loftusia ; but its absence 

 cannot be certainly affirmed. In fully grown specimens the turns of the 

 spire, which succeed each other with tolerable regularity at intervals of 

 from 1-5 Oth to I -30th of an inch, are usually from twelve to twenty in 

 number ; but as many as twenty-five have been counted in one instance, 

 and a yet larger number might not improbably be met with. The spiral 

 lamina and its prolongations, forming the accessory skeleton, are all con- 

 structed of almost impalpable grains of sand, which is proved by analysis 

 to have consisted of Carbonate of Lime, united by a cement of the same 

 material. 



The Author then describes in detail the several components of the fabric 

 of Loftusia, and compares them with the corresponding parts of Parkeria. 

 The continuity of increase of the spiral lamina always leaves an open fissure 

 between its last-formed margin and the surface of the previous whorl ; and 

 through this aperture the whole system of chambers included within its 

 successive laminse communicates with the exterior, through the passages 

 between their cavities, which are left in the building up of the septa. As 

 already explained, the labyrinthic structure takes its origin from the inner 

 surface of the impervious spiral lamina, the septa being directed towards 

 the central axis. These ingrowths have in many instances the form of 

 tubular columns, which traverse the chambers in a radial direction [i. e. 

 perpendicular to the spiral lamina), terminating either on the septum of 

 the previous chamber, or on the exterior wall of the preceding whorl of 

 chambers. But these tubes do not seem to be homologous with the tl radial 

 tubes" of Parkeria, whose relations differ in important particulars. The 

 range of variation in a number of specimens, as to the amount of the 

 "secondary" and "tertiary" ingrowths which divide and subdivide the 

 chambers in Loftusia is very great. The principal office fulfilled by this 

 accessory skeleton seems to be that of a support to the primary spiral 

 lamina, imparting the necessary solidity to the organism. The degree of 

 subdivision of the chambers into chamberlets seems to have little bearing 

 on the general economy of the animal. 



The Author attempts to determine from the other Foraminifera, of 

 which the remains are found associated in the same Limestone with those 

 of Loftusia, what was its probable Geological age, and under what condi- 

 tions it was deposited ; and he thence draws the conclusion that the rock 

 belongs to the lowest portion of the Tertiary period, presenting a microzoic 

 Fauna very similar to that of some of our Miliolite Limestones, but richer 

 in the small arenaceous Rhizopods ; and that the sea-bottom was a soft 

 Calcareous mud lying at a depth of from 90 to 100 fathoms. 



