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FAMILY MILIOLIDA 



modes of communication between the chambers of the two types, and that such a difference is 

 sufficiently important to constitute a vahd generic character. I freely admit that this would 

 be the case, if the difference were constantly to present itself between all the individuals of the 

 same type, as it does between their characteristic examples (Plate VII, figs. 13, 16); but the 

 fact is far otherwise. We have seen that among those which would be unhesitatingly ranked 

 under the designation Feneroplis, there is not only a tendency to multiplication of the rows of 

 separate pores, but also an occasional fusion of two or more pores, so as to form a single large 

 pore of irregular shape. On the other hand, among the unquestioned DeiidritincB we observe 

 not merely that the form of the single large dendritic aperture is extremely variable, but that 

 it is frequently so simple as to suggest the idea of having been formed by the coalescence of a 

 linear series of pores. The highest development of the dendritic form of aperture that I have 

 met with, is shown in fig. 14, a, b ; two examples of a remarkable departure from this have 

 just been seen in Fig. XX, b, d, where the proportions of the aperture are altogether 

 reversed, its breadth being much greater than its length, and its central part being enlarged 

 at the expense of its ramifications ; while, on the other hand, in Fig. XX, a, c, we have 

 marked examples of a narrowing and elongation of the aperture, with such a reduction 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 (fig. 13) that presented the peculiarly characteristic example represented in 

 fig. 14, we find a form of aperture closely corresponding to that shown in Fig. XX, c ; and 

 in four septa of the inner part of another shell we have the simple forms of aperture repre- 

 sented in Fig. XXI, a, b, c, d. 



Fig. XXI. 



A. ■ ^ B 



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



l30. But further, not only do we thus meet with examples of each type which present 

 more or less of approximation towards the other, but we also not unfrequently encounter 



