334 



contact, or complete osculation, with the given cubic. It is shown 

 that the points in question are those which are their own third 

 tangentials, and this suggests the consideration of the new canonical 

 form, x^y+y^z + z^x + Vmxyz^Q, of the equation of the cubic; this 

 inquiry, however, is not pursued in the paper. 



XX. " Researches on the Foraminifera." Part III. On the 

 Genera Peneroplis, Operculina, and Amphistegina. By W. 

 B. CARPENTER, M.D., F.R.S. &c. Received June 17, 1858, 

 (Abstract.) 



In his preceding memoirs, the author has shown that two very 

 dissimilar types of structure present themselves among Foraminifera, 

 one characterized by its simplicity, the other by its complexity. In 

 the former, of which Orbitolites, Orbiculina, and Alveolina are typi- 

 cal examples, the calcareous skeleton does not present any definite 

 indications of organization, but seems to have been formed by the 

 simple calcification of a portion of the homogeneous sarcode-body 

 of the animal ; that sarcode-body is but very imperfectly divided 

 into segments, the communications between the cavities occupied 

 by these segments being very free and irregular ; the form of the 

 segments themselves, and the mode of their connexion, are alike in- 

 constant ; and even the plan of growth, on which the character of 

 the organism as a whole depends, though preserving a general uni- 

 formity, is by no means invariably maintained. In the latter, to 

 which Cyclodypeus and Heterostegina belong, the calcareous skele- 

 ton is found to present a very definite and elaborate organization. 

 The several segments of the body are so completely separated from 

 each other, that they remain connected only by delicate threads of 

 sarcode. Each segment thus isolated has its own proper calcareous 

 envelope, which seems to be moulded (as it were) upon it ; and this 

 envelope or shell is perforated with minute parallel tubuli closely 

 resembling those of dentine, except in the absence of bifurcation ; 

 the partition-walls between adjacent segments are consequently 

 double, and are strengthened by an intermediate calcareous deposit, 

 which is traversed by a system of inosculating passages that seems 

 properly to belong to it. The form of the segments, their mode of 



