NAUTILIDJ3. 
337 
laacet-shaped lobe on each side.” In the 3rd (enlarged) edition 
(Band iii. 1856, p. 595) he describes the siphuncle as nothing 
more than a funnel-like prolongation of the septa, the extremity of 
which penetrates deeply into the immediately preceding funnel, 
with the interior of which it is united, being thickened at the point 
of junction. From the strong contraction of the siphuncle it fol- 
lows that, although its aperture rests on the edge of the septa, its 
narrow extremity is not in contact with the shell-wall. In this 
respect the siphuncle of Aturia differs from that of Clymenia and the 
Ammonites. 
Aturia may now be defined as follows: — Shell Nautilus-like, 
compressed, completely involute, non-umbilicated. Septa numerous, 
with an angular lobe on each side, directed backwards, and abutting 
against the shell-wall (fig. 72, Z) ; the dorsal part of the septa pro- 
longed backwards and forming a large, marginal, funnel-shaped 
siphuncle (fig. 72, s). 
Type, Nautilus Aturi^ Basterotk 
Eocene to Miocene. 
RemarJcs. The remarkable feature in the siphuncle of Aturia is 
the great length of the septal necks. These form a series of in- 
vaginated funnels ^ which are slightly constricted at their narrower 
or posterior extremity, just after they emerge from the mouth or 
opening of the preceding neck ; at which point they form a swollen 
band or collar (fig. 72, c), on or a little posterior to which there is a 
suture line, which marks the commencement of the nacreous layer 
at its narrow end, or, in other words, the beginning of a new 
septal neck. The “ couche jaune,” which will be called in future 
the yellow layer, spreads over the whole of the internal wall of 
the siphuncle, and is separated from the thick nacreous shell 
by a porous layer, about to be described. The surface of the yellow 
layer is smooth, or very slightly rugose in places. On removing 
portions of the thick nacreous layer (fig. 73, 5, 6 & c, c) a porous 
layer ^ is seen (fig. 73, e, e & y')-, which is thickest at or near 
“ Descrip, de.s Coquilles Fossiles des En-virons de Bordeaux,” Mem. de la 
Soc. d’Hist. Nat. de Paris, vol. ii. 1825, pt. i. p. 17. 
^ The term “funnel ” is not employed here in a technical sense, but only as 
expressing the form of these prolongations of the septa. In a strict sense they 
Will always be called “ necks,” the English equivalent of the French term 
“goulots,” and of the German “ Siphonalduten ” or “ Septaldiiten.” 
^ A similar layer to this one was described in Nautilus 'pompilius by Quenstedt 
as “ poriisen Kalksinterschicht (‘ Die Cephalopoden/ 1849, p. 23); by Valenci- 
ennes under the name of mucoso-calcaire (Barrande misquotes the last word 
PAET II. 
Z 
