hydraulic action of siphuncle. 
351 
iHode of operation as a pipe, admitting or reject- 
a fluid, seems to have been the same as that 
have already considered in the case of Nau- 
tili.* 
The universal prevalence of such delicate 
^‘ydraulic contrivances in the Siphuncle, and of 
Such undeviating and systematic union of buoy- 
'^ucy and strength in the air-chamhers, through- 
out the entire family of Ammonites and Nautili, 
ure among the most prominent instances of order 
uud method, that pervade these remains of former 
In the family of Ammonites, the place of the Siphuncle is 
'Uvvays upon the exterior, or dorsal margin of tlie transverse plates. 
(See PI 3 ( 5 . f]. g. f. g. h. i., and PI, 42, Fig. 3. a, b.) It is 
Conducted through them by a ring, or collar, projecting oatwarclj-; 
Uiis collar is seen, well preserved, at the margin of all tlie trans- 
yei'se plates in PI. 36. In Nautili, the collar projects uniformly 
'^'^'toards, and its place, is either at the centre, or near the inrier 
‘'‘Margin of the transverse plates. (See PI. 31, Fig, 1. y. and 
Pi- 42. 1.) 
The Siphuncle represented at PI. 36, is preserved in a black 
'Carbonaceous state, and passes from the bottom of the external 
^I'amber (d.) to the inner extremity of the shell. At e. f. g. h. its 
nuerior is exposed by section, and appears fdicd, like the adjacent 
^^-chambers, with a cast of pure calcareous spar. At PI. 42. 
. g- 3. b. a similar cast fills the tube of the Siphuncle, and also the 
^“■-chambers. Here again, as in PI. 36, its diameter is con- 
l^cted at its passage through the collar of each transverse plate, 
"'ith the same mechanical advantages as in the Nautilus. 
The shell engraved at PI. 42. Fig. 4. from a specimen found by 
® Marcpiis of Northampton in the Green sand of Earl Stoke, 
**®^r Devizes, and of which Figs. 5. 6. are fragments, is remark- 
® for the preservation of its Siphuncle, distended and empty, 
still fixed in its place along the interior of the dorsal margin 
Uie shell. This Siphuncle, and also the shell and transverse. 
