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 poste- 
rior 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. Da Costa also, in his “ Elements of 
Conchology,” says, “ I have seen fossil kinds with foliaceous sutures, 
like the ammonitae ; 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 in- 
formation. 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, mea- 
sures full nine inches in its longest, and seven inches in its shortest, 
diameter. But the most striking character which it offers to our ob- 
servation 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 corresponding lobated process of the next anterior 
septum. 
VOL. III. p 
