166 
NAUTILOIDEA. 
The shelly covering of these segments, which is composed of several 
layers, is very rarely preserved h The calcified lining membrane of 
the siphuncle is thrown into a series of folds which impart to it a 
puckered appearance which is very characteristic. The endo- 
siphon is provided with a distinct wall and gives off at regular in- 
tervals between the septa a number of radiating canals or tubuli 
which apparently penetrate the shelly covering or wall of the 
siphuncle, and, if so, they may have served, as suggested by Owen^, 
for the passage of blood-vessels to the lining membrane of the septal 
chambers. The spaces between the tubuli are sometimes filled up so 
that curved transverse partitions, which are formed originally iu 
membrane, and are convex anteriorly, divide the siphuncle into a 
series of loculi. Xothing is seen of these partitions when tho 
siphuncular cavity has been filled with calc-spar. 
The first segment of the siphuncle is in the form of a broadly 
conical chamber, perforated above the apex by a large foramen, 
through which the eodosiphon passed from the initial chamber into 
the siphuncular cavity ® (figs. 22, 23). 
CAMBPJA^^ SPECIES. 
Actinoceras ? mendax, Salter. 
1859. Orthoceras mendax^ Salter, Quart. Journ. Geol. Soc. vol. xv. 
p. 374, pL xiii. f. 24, a, b. 
1882. Orthoceras mendax, Blake, British Foss. Ceph. pt. i. p. 81, pi. iii. 
f. 1. 
Sp. Char. “ General form very gradually tapering, with shallow 
close annulations (J of an inch apart in a diameter of f of an 
inch) in the older portion, in the young nearly smooth. Section 
circular. Septa numerous, close-set, one to each aunulation in the 
older part ; at a diameter of 4 lines there are 15 to an inch. They 
are only slightly concave, and bent down somewhat angularly 
towards the siphuncle, which is excentric, thick, smooth-edged 
(not at aU beaded), and compressed in a direction from front to 
back. It also has a shaUo;w groove along the side nearest to the 
^ Bigsby {Joe. cit. p. 202). A specimen of Ruronia in the National Collec- 
tion (Jso. 36088, presented by Dr. Bigsby) shows this shelly investment very 
distinctly. 
2 This may be seen in a specimen in the Collection registered C 2142. 
3 Bronn estimates their number to be about sixteen, but they certainly exceed 
this in some examples, as the number of foramina testify. 
^ Paleontology, 1860, p. 85. 
Cf. Filoceras, p. 159. 
