8 DE. CAEPENTEE'S EESEAECHES OX THE FOEAMINIFEEA. 



excite surprise to find that Peneroplis, like Orbiculina, presents very considerable diver- 

 sities of conformation. The first and simplest departure from what has been described as 

 its typical character, consists in a duplication of the series of pores in each septum 

 (Plate II. fig. 7 a), the spire being at the same time less compressed, so that the septal 

 plane is wider in proportion to its length. Now it is not a little remarkable that this is 

 almost uniformly the case with specimens furnished by particular localities, whilst those 

 obtained from others not very remote exhibit almost as uniformly the extremest elonga- 

 tion and narrowing of the septal plane with only a single row of apertures ; and hence 

 it might not unreasonably be maintained that this difference should be accounted of 

 specific value. In reply to this, however, there is not only the analogy of Orbitolites 

 and Orbiculina, in which an indefinite multiplication in the rows of marginal pores may 

 take place during the growth of the individual, but also the fact that in Peneroplis the 

 two forms cannot be distinguished at an early age, either by the shape of the shell or 

 by the disposition of the pores, which are often arranged neither in a single nor in a 

 double row, but on a sort of mixture of both plans, as shown in Plate II. figs. 9 and 10 ; 

 whilst among the more advanced examples of each type, it is not at all uncommon to 

 meet with individuals which present a combination of the characters of both, the septal 

 plane having a single row of pores in one part of its length with a double row in another. 

 Sometimes, moreover, in one of the less compressed forms of the shell, although there 

 is but a single row of pores, it is obvious from the elongated shape of these that they 

 indicate a tendency to duplication (fig. 8). Moreover we find in the variety with a com- 

 plete double row the same disposition as in the ordinary Peneroplis to the substitution 

 of the rectilineal for the spiral mode of growth, as we see in fig. 7. Hence I consider 

 that it may be unhesitatingly asserted that the duplication of the row of pores, and the 

 increased turgidity of the spire which it accompanies, are but features of individual 

 variation, and cannot be admitted to rank as specific differences. And in this view I am 

 glad to find myself borne out by Professor WILLIAMSON, who defines Peneroplis*, not 

 (like M. D'ORBIGNT) as having only a single row of apertures, but as having " septal 

 orifices scattered over the long narrow septal plane ; " whilst his figure of Peneroplis 

 planatus shows these orifices arranged for the most part in a double row, one portion 

 having them even more multiplied. 



132. What is the relationship to the typical Peneroplis, however, of that group of 

 forms to which D'ORBIGNY has given the generic designation Dendritina, is a question 

 of more difficulty. These are characterized, as we have seen, by the possession of a 

 single large aperture sending out dendritic ramifications in each septum (Plate I. fig. 1, 

 Plate II. figs. 12, 13) ; but this is by no means the whole of their differentiation. For 

 the spire, instead of being compressed, is very turgid ; and its successive whorls not 

 merely surround but also invest those which have preceded them ; so that what may be 

 appropriately termed alar prolongations (al, figs. 12 a, 12 b, Plate II.) of the chambers of 

 even the last whorl often extend nearly to the umbilicus. The geographical distribution 



* The Eecent Foraminifera of Great Britain, p. 44. 



