552 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



having many such floorSj with numerous rows of marginal pores. In the former, the 

 segments of sarcode, with their single annular stolon, would resemble rounded beads 

 strung at short distances on a cord. In the latter the segments would be columnar, 

 with constrictions at intervals, and would communicate with each other by two or 

 more annular stolons. It is true that we seldom find any such complete differentia- 

 tion of the superficial cells, as the fully-developed type of Orbitolites presents; but 

 we have seen that such differentiation is by no means a constant character in that 

 genus (^[58); and the structure of the most developed specimens I have examined 

 among the recent Orbiculince closely corresponds in this respect with that of the 

 fossil Orbitolites of the Paris basin, as will be seen on comparing the left-hand portion 

 of Plate XXIX. fig. 3 with Plate VI. fig. 1 1 of my former memoir. But it is not a 

 little remarkable, that while the fossil Orbitolites of the Paris tertiaries are less deve- 

 loped in this respect than their existing representatives in the South Seas, the fossil 

 Orbiculince of the Malabar tertiaries should be more developed than existing speci- 

 mens of the same type; for in them we find the superficial cells differentiated from 

 the intermediate layers (Plate XXVIII. fig. 20), precisely as in Orbitolites*. Looking 

 to the far larger dimensions, as well as to the higher development, which these fossils 

 present (^[83), as compared with the existing specimens of Orbiculina, I am disposed 

 to believe that this type attained its highest evolution in a period long since passed, 

 and that we now have, so to speak, only the degenerate descendants of an ancestry of 

 higher rank; whilst in the case of Orbitolites, I am inclined to think that the type is 

 most fully evolved at the present time. 



91. General conclusion. From the foregoing details it is obvious that the relation- 

 ship between Orbitolites and Orbiculina is extremely close ; the only essential point 

 of difference between them being that which is furnished by the structure of the 

 nucleus. Whether or not they ought to rank as types of distinct genera, or whether 

 they ought (as Professor WILLIAMSON maintains) to rank as cognate species of the same 

 genus, is a point as to which it is impossible to arrive at a satisfactory conclusion, 

 until the characters which should serve for the distinction of genera and species in 

 this class shall have been determined on a physiological basis. This much I think 

 myself entitled to assert with confidence, that even if they are to be regarded as 

 distinct genera, they must be ranked in the same family, and in immediate proximity 

 to each other ; and that no classification can have any claim to be considered as 

 natural, in which they shall be widely separated. 



Genus ALVEOLINA. 



92. History. Although the form and aspect of the Foraminifera which are refer- 

 able to this genus, would seem to remove them altogether from proximity to the pre- 



* Although Mr. CARTER has described this fossil as a species of Orbitolites, yet it is really an Orbiculina, as 

 is shown by the spiral conformation of its central portion (Plate XXVIII. fig. 17), and by the investment 

 afforded by each turn of the spire to its predecessor, as shown in fig. 18. 



