164 



are not absorbed, but remain projecting into the cavities of the subse- 

 quently formed chambers. 



After making numerous sections of these shells, I found that what, 

 externally, constituted the elevated folds or ridges in the transverse 

 undulations of each segment (fig. 1,6, and 3, a), internally formed cor- 

 responding grooves (fig. 4, a), shallowed anteriorly, but deepening pos- 

 teriorly, and before coming in contact with the septum in front of the 

 antecedent cell (fig. 4, c), each receiving from that septum a small in- 

 ternal lamella (fig. 4, b), which for a short space converts them into 

 perfect tubes (fig. 3, c and 4, d). To the left hand of the latter 

 figure, the section has removed these inner plates and laid open the 

 tubes. These do not penetrate the septum or form open channels 

 of communication with the antecedent chamber; their extremities 

 merely rest against it (fig. 4, e). On breaking into this adjoining 

 chamber in thin and transparent specimens, and looking at the inner 

 surface of its anterior septum, the circular outlines of these tubes 

 may be seen through the hyaline diaphragm, which, however, closes 

 them in. 



On removing the whole of the front and lateral parietes of any one 

 chamber, we find the positions of the extremities of these tubes repre- 

 sented on the front of the posterior calcareous septum, where we see 

 an arched marginal series of circular depressions (fig. 5, a). These 

 depressions do not appear to have been formed by the excavation 

 or thinning of the septum ; after a variety of examinations, I have 

 satisfied myself that each septum separating two cells, consists of 

 a double calcareous layer, — the soft inhabitant of each segment 

 secreting its own share. The depressions appear to be formed by the 

 absence of the second layer at the points opposite to the termination 

 of the tubes, where the septum apparently consists only of a single 

 layer, contributed by the antecedent segment of the animal. 



Along the inner margin of each of these internal septa where it ad- 

 joins the next inner convolution, we find an arched row of apertures 

 perforating the septum, in the position occupied by those already 

 alluded to as being occasionally visible in the front of the first 

 or outermost chamber (fig. 5, b). They are, however, much more dis- 

 tinct in the former than in the latter. 



The microscopic texture of the shell is curious. It appears to be 

 crowded with myriads of minute foramina, and in addition to this, it 

 is evidently shagreened — covered over with small pointed tubercles 

 (fig. 4,/), which, from the rounded form of their bases, may be easily 

 mistaken for foramina, when the shell is mounted in Canada balsam, 



