8 DE. CAEPENTEE’S EESEAECHES ON THE EOEAIVnNIFEEA. 
excite surprise to tod that Penero],lh, like OrWmlma, presents very considerable diver- 
sities of conformation. The first and simplest departure Irom what has been des^cnbe as 
its typical character, consists in a duplication of the series of pores m each sept,m 
(Plate 11 fig. 7«), the spire being at the same time less compressed, so that the septal 
5^!:!ris wideV inUortion to its length. Now it is not a little remarkable that tto rs 
almost uniformly the case with specimens furnished by particular locahties, whdst those 
obtained from others not very remote exhibit almost as uniformly the extremest elonga- 
tion and nairowing of the septal plane with only a single row of apertm-es, and ence 
it might not unreasonably be maintained that this difference should be 
specific value. In reply to this, however, there is not only the analogy of OrhUUeB 
mid OrUculma, 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 ^ 
two forms cannot be distinguished at an early age, either by the shape of the sheU 
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 m Plate I . gs. an , 
whilst among the more advanced examples of each type, it is not at all uncommon o 
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 doub e row in anote 
Lmetimes, 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 y 
indicate a tendency to dupUcation (fig. 8). Moreover we find in the variety- with a com- 
nlete double row the same disposition as in the ordinary Pmeroplis to the substitution 
of the rectilineal for the spiral mode of growth, as we see in fig. 7. Hence I “nsi er 
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 featoes of individual 
variation, and cannot be admitted to rank as specific differences. And in this v-imv I am 
glad to find myself borne out by Professor Williamson, who defines Penerophs , not 
(like M. d’Oebiony) as having only a single row of apertures, but as kavmg sep a 
orifices scattered over the long narrow septal plane;” whilst his figure .iPeneropks 
plmatm shows these orifices arranged for the most part m a double row, one portion 
liavinff them even more multiplied. ^ ^ r 
132 What is the relationship to the typical Pmeroplis however, of that gioup of 
foims to which D’Okbignt has given the generic designation Vendnttna, is a question 
of more difficulty. These are characterized, as we have seen, by the possession o a 
single large aperture sending out dendritic ramifications in each septum (Plate I. fig^ , 
Plate II figs 12 13) ; but this is by no means the whole of then differentiation. Foi 
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 
approUtely termed alar prolongations (al, figs. 12 «, 12 b, Plate II.) of Ae chamber of 
even the last whorl often extend nearly to the umbilicus. The geographical distribution 
* The Eecent Eoramiaifera of G-reat Britain, p. 44. 
