EELATION OF DENDEITINA TO PENEEOPLIS. 
11 
of its dendritic ramifications, that it comes to present little more than a linear fissure. 
From a comparison of these cases, it will be seen that the form of the aperture bears 
a pretty constant relation to that of the septal plane ; the broadest apertures presenting 
themselves in the individuals which have the most turgid spire, and the narrowest in 
those whose sphe is most compressed ; whilst the proportionate development of the two 
principal alar prolongations seems related to the degree of that alar extension of the 
chambers over the whorl they enclose, of which I have already spoken. But the most 
satisfactory proof of the wide extent of range of variation in the form of the aperture 
in Bendritina, is afforded by a comparative examination of the apertures connecting 
different chambers of the same individual. Thus in the interior of the very shell that 
presented the peculiarly characteristic example, Plate II. fig. 12 a, we find a form, 5, 
closely corresponding to that shown in Fig. II. c ; and in four septa of the inner part of 
another shell, we have the simple forms of aperture represented in Fig. III. A, B, c, d. 
Eig. III. 
Septal planes and apertures from different parts of the same specimen of Dend/ritina. 
137. But further, not only do we thus meet with examples of each type which pre- 
sent more or less of approximation towards the other, but we also not unfrequently 
encounter indhiduals in which the characters of the two types are so blended that it is 
difficult, if not impossible, to say to which they should be referred. Thus in Plate II. 
fig. 8, we have a young specimen with a linear series of apertures, the marked elongation 
of which show's each to be formed by the fusion of two, whilst there is an additional pair 
precisely in the situation of the alar prolongations in fig. 12 ^ ; and it is obvious that a 
longitudinal coalescence of these pores would produce an aperture exactly resembling 
that of fig. 12 h. Again, in another young specimen shown in Plate II. fig. 16, a partial 
fusion of the separate pores into a single dendritic aperture has actually taken place 
(fig. 16 «), w'hilst another broad aperture is seen just below this. In fig. 10 we see 
numerous pores, some small and rounded, others large and irregular, each of the latter 
being ob\dously formed by the coalescence of two or three of the separate pores ; and it 
is eAident that a closer approximation of the whole would produce a single large den- 
dritic aperture. Other varieties of the same kind are presented in figs. 9 and 14. But 
a yet more remarkable example is shown in fig. 15 ; for here the coalescence has pro- 
c 2 
