105 



actually depressed in its centre. A specimen of this species, which I 

 possess, is a German fossil : the siphunculus, in this specimen, runs 

 about midway between the middle of the chamber and its inner side. 

 The line, Plate VII. Fig. 13, is that which is described by its posterior 

 surface. 



Breynius had observed, that all nautili did not agree in the form of 

 their septa; and hence divides them into two orders: 1st. Those with 

 concavo-convex semilunar diaphragms; and, 2dly, Those with jagged 

 or sinuated diaphragms. Dacosta also, in his " Elements of Con- 

 chology," says, " I have seen fossil kinds with foliaceous sutures, like the 

 ammonitse; which implies, that all the species have not such regular 

 roundish partitions." P. 168. 



The fossil shell of this description which appears to be the most 

 uncommon of those which I have seen; differing the most widely of any, 

 not only from the recent, but from the other fossil nautili, is one, of 

 which I purchased the remains at the sale of Dr. Menish's collection. 

 Of the place where this fossil was obtained, I have no information : its 

 striking characters are, its great size, the situation of its siphunculus, and 

 the peculiar form of its septa, and of course of its chambers. Plate VII. 

 Fig. 15, is an outline sketch of this fossil, one third of the size of the 

 original. 



The outermost septum in this specimen, which is not that which was 

 the last, and consequently the largest, of the original shell, measures 

 full nine inches in its longest, and seven inches in its shortest diameter. 

 But the most striking character which it offers to our observation is, the 

 form of the septa ; since these, instead of having a regular rounded 

 sweep, as in the recent nautili, and in most of the fossil species, have 

 an undulated form. This results from each septum forming a deep 

 lobated process, extending backwards, on each side, over which process 

 is hollowed out a deep sinuous notch, for the reception of the cor- 

 responding lobated process of the next anterior septum. 



VOL. III. P 



