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SUPPLE ilEXT. 
that shape which for so long a time has been alone known as the 
Ascoceras. There are thus two stages to be taken into consideration 
separately in a description, viz. (1 ) the Xautiloid ; (2) the Ascoceras 
proper. 
(1) The Nautiloid (Fig. 84, F, n ). — I have called this stage so, 
because it corresponds with the common type of the suborder of 
the J^autiloidea. It cannot properly be called an Orthoceratite stage 
as the shell is not straight, but curved and thus rather a Cffrtocei'aa, 
having also the siphuncle formed in accordance with that genus. If 
it ever was quite entire and intact, before attaining its last [Asco- 
ceras] stage, the shell has been bent in a large arch (fig. 84, F, u) ; 
but it is evident that it broke off and was decollated several times 
during its growth. In some species (Asc. Jistida), the Nautiloid part 
was straighter, though slightly curved. The thin shell, which onl)’ 
slowly widened, is generally transversely striated or annulatcd, with 
slight modifications in the different species. The interior structure 
is highly uniform in all, with oblique watchglass-like septa, higher 
on the dorsal side than on the ventral ; placed at very irregular 
distances from each other, sometimes close, sometimes wide apart, 
the distance increasing with the augmenting width of the shell. 
The siphuncle is always placed near the ventral side, and consists of 
tubular, narrow elements, enclosed in a calcareous sheath of their 
own, and connected with the funnel of the downwardly curved septal 
aperture [neck]. In some there is a tube on the upper surface of 
the septum, which encloses the base of each siphonal element. 
2. The Ascoceras proper (Fig. 84, A, E, and upper part of F). — 
The shell, often pyriform or flask-shaped, consists of two different 
portions — the lower or larger, usually wider portion, containing the 
septa, and its more narrow, neck-like continuation, ending with the 
round aperture. The shell is almost always flattened from two 
opposite sides, in the lower or essential portion with an ovate sec- 
tion, and cylindrical in the neck with circular section. There are 
two difiPerent sorts of septa: (1) Eegular, Nautiloid septa; (2) 
Sigmoid, Ascocerate septa proper. The first septum, which may be 
regarded as the last Nautiloid septum and forms the bottom of the 
shell, is strengthened from within by organic deposits of calcareous 
matter. It is in a distinct group of species followed by a second 
septum of regular shape ; but in the majority of species the abnormal 
sigmoid septa follow immediately on the first. The number of the 
sigmoid septa varies from three to seven, but is very constant in the 
same species. A fragmentary specimen of an unknown species has 
indications of no less than twelve septa. The septa are continuous 
