24 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 2, 



ceding whorl, was first stated, 1 believe, by M. D'Orbigny (Annales 

 des Sciences Naturelles, 1826, tome vii. p. 295). This aperture, 

 which was correctly figured — I believe for the first time — by Mr. 

 Sowerby (Mineral Conchology, vol. vi. p. 73. tab. 538), is best 

 brought into view by fracturing a Nummulite in a direction perpen- 

 dicular to that of the preceding sections, so as to present a broken 

 edge, of which about one-half is shown in fig. 4. On looking into 

 the chambers which are thus laid open, along the line a a\ we are of 

 course stopped by the septa 5, hy each of which is seen to present an 

 aperture c, c, where it abuts against the margin of the preceding 

 whorl. From the examination of specimens fractured in various di- 

 rections, I am quite satisfied that these perforations pass through both 

 layers of each septum, so as to establish a free communication be- 

 tween one chamber and another. The case is different, however, 

 with regard to certain more minute apertures, (not discerned, I be- 

 heve, by any previous observer,) which may be seen, by a careful 

 examination under a sufiicient magnifying power, to exist on the sur- 

 face of every septum, though not constant either in number or position 

 (see fig. 7, «). I at first believed that these also pass from chamber 

 to chamber ; but I am now satisfied that they penetrate that layer 

 only of the septum, on whose surface they open, and that they really 

 establish a communication between each chamber and the adjoining 

 interseptal spaces. Other apertures of the same kind may be gene- 

 rally traced, on careful examination, in those walls of the chambers 

 that form the surface of the whorl ; and these, too, appear to com- 

 municate with the interseptal spaces, by channels burrowed in those 

 walls, as shown in the lower part of fig. 6, and also in fig. 16, in 

 which last they are represented as seen in a thin section of the roof 

 of the chambers. 



Thus the cavity of each chamber communicates with that of the 

 one before and behind it in the same whorl, by the large aperture 

 first mentioned, which frequently appears as if made up by the coa- 

 lescence of a number of smaller perforations (fig. 7, ^), suggesting 

 the idea that the animal substance which originally passed through 

 it was not a single large canal, but was composed of a bmidle of mi- 

 nuter tubes or threads. This idea is confirmed by the circumstance, 

 that the outer margin of the included whorl (fig. 7, c) frequently 

 presents a series of furrows, corresponding to the notches at the 

 inner edge of the septum (6) . Each cavity also communicates freely 

 with the interseptal spaces on either side, by the smaller apertures 

 and passages last described ; and from this space, as we shall pre- 

 sently see, there was a free passage to the external surface of the 

 shell. 



The texture of the shell itself differs remarkably from that of any 

 of the Mollusca with which I am acquainted, approaching that which 

 I have described in the common Crab (Reports of the British Asso- 

 ciation, 1847, p. 129). It is everywhere perforated by a series of 

 tubes of extreme minuteness, which pass directly from one surface to 

 the other, their openings being plainly visible on each (fig. 16). 

 The diameter of these tubes is about 1 -7500th of an inch ; and their 



