KELATION OF DENDEITINA TO PENEKOPLIS. 



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 spire 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 Dendritina, 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, b, 

 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. 



Fig. III. 



Septal planes and apertures from different parts of the same specimen of Dendritina. 



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 individuals 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 shows each to be formed by the fusion of two, whilst there is an additional pair 

 precisely hi the situation of the alar prolongations in fig. 12 b ; and it is obvious that a 

 longitudinal coalescence of these pores would produce an aperture exactly resembling 

 that of fig. 12 b. 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 ), whilst 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 obviously formed by the coalescence of two or three of the separate pores ; and it 

 is evident 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- 



c2 



