32 DE. CAEPENTER'S EESEAECHES ON THE FOEAMINIFEEA. 



meter of the recent specimens does not elsewhere exceed -065 inch, it attains in some of 

 the Philippine examples as much as -115 inch, thus equalling that of the largest fossil 

 specimens which have come under my notice. The general correctness of Professor 

 WILLIAMSON'S description of this species I can fully confirm ; but the comparison of a 

 large number of sections leads me to the unhesitating conclusion that the inequilaterality 

 which has been considered the distinctive character of this type is so inconstant, as to 

 forbid our assigning any value to it as a generic, still less as an ordinal character. It is 

 often very strongly marked in the fossil Amphistegince of the Vienna and St. Domingo 

 tertiaries ; but it is as frequently absent altogether, the shell being perfectly equilateral ; 

 and between these two extremes of form we find every intermediate gradation. So it 

 frequently presents itself among the small specimens of Amphistegina gibbosa which are 

 common in tropical seas, and I have met with specimens exhibiting as great a want of 

 symmetry as the one of which Professor WILLIAMSON has delineated a section ; yet on 

 the whole, I should say, that in the great bulk of the smaller specimens which have 

 passed under my notice, the want of symmetry is but slight ; whilst perfect equilaterality 

 both of external form and of internal arrangement not unfrequently occurs ; and in those 

 large specimens from the Philippines which present this type in its highest development, 

 there is little or no departure from exact symmetry. But further, Mr. CUMING'S collection 

 furnishes numerous examples of a remarkable species whose general conformity of 

 structure to Amphistegina gibbosa seems to leave no doubt of its near relationship to it 

 (the resemblance of its younger specimens to that specific type being so close as to have 

 led me in the first instance to a belief in the specific identity of the two), and yet the 

 most exact symmetry here presents itself as the rule, departures from it being excep- 

 tional, and never proceeding to any considerable extent. It may be considered, there- 

 fore, as satisfactorily established, that want of lateral symmetry is not to be held as an 

 essential character of the shells of this genus, although more frequently occurring in it 

 than in Nummulites or Operculina, to which, as I shall now show, this type bears an 

 extremely close relationship. 



167. The species to which I have just referred being hitherto undescribed, I shall 

 designate it A. Cumingii. In its young state it is lenticular in form (Plate V. figs. 13, 14), 

 and is only distinguishable from the symmetrical variety of A. gibbosa by the smaller 

 number and greater angular distance of the septal bands which radiate from the centre 

 and suddenly turn backwards as they approach the margin. (The radiating portions of 

 these septal bands, as will presently appear, mark the direction of the portions of the 

 septa that intervene between the alar prolongations of the chambers ; whilst the recur- 

 rent portions mark the direction of the portions of septa that separate the principal 

 cavities of the chambers.) As the A. Cumingii advances in life, however, a marked 

 change presents itself in its form, corresponding to that which I have shown to occur in 

 Heterostegina, Peneroplis, and Operculina; for the spire, after about its fourth turn, 

 begins to flatten itself out, and separates itself henceforth from the central portion of 

 the shell, to which it affords a very partial investment (figs. 15-17), the spiral lamina 



