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of the newer convolution, in which the septa are more numerous. 

 Small circular apertures appear along the course of these tubes, and 

 mark as many points where the section has traversed the orifices of 

 the canals, descending to the inferior surface of the shell. A third 

 section, made parallel to the foregoing, is cut through the shell a little 

 above the superior extremities of cells belonging to the central con- 

 volutions. We here see that the portions which, in the former 

 section, had the appearance of radiating tubes, are really the lower 

 borders of vertical iuterseptal spaces, but at the same time giving off 

 true divergent cylindrical canals from their external margins, which 

 penetrate the thick parietes of the shell. Whilst these spaces com- 

 municate externally, they open internally into a large irregular cavity, 

 the true nature of which is better understood by reference to a verti- 

 cal section of this instructive object passing nearly through its centre; 

 this section, if it has not traversed the primordial cell, has certainly 

 crossed the second one, along with four others, in the successive order 

 of their development. Whilst their inferior portions are nearly on a 

 uniform level, the upper extremities of those belonging to successive 

 convolutions become rapidly elongated, leaving between them a large, 

 irregular, conical space. In the species under consideration a new 

 and curious feature is presented : the cavities in the translucent cal- 

 careous shell are thickly lined with a dark olive- brown substance ; 

 this substance not only exists in the interior of all the cells, but also 

 occupies the intraseptal spaces and their respective canals, as well as 

 the irregular cavity in the umbilical centre of the shell. It is most 

 probable that this brown substance is really the desiccated soft ani- 

 mal. A thin superficial section, made in the plane of the oblique 

 sides of the conical shell, exhibits some of the septa with the large 

 orifices of their iuterseptal canals, with the external parietes of some 

 of the segments densely perforated with minute pseudopodian fora- 

 mina, and a small lateral portion of the dome-like apex of the shell, 

 which is perforated with apertures, through which a free communica- 

 tion is maintained between the external medium and the inclosed 

 space. The nature of the latter varies considerably ; sometimes it 

 exists in the form of a large irregular cavity, and at others as an intri- 

 cate network of large canals. The character of the external orifices 

 also varies : in some examples they are large and patent ; in others, 

 numerous smaller tubes, ascending from the subjacent network, con- 

 verge at some superficial depressions which occupy the position of 

 the larger orifices. 



The above facts show that the subject of the present memoir pre- 



