NATJTILTDJE. 
341 
Aturia, and similar structures in Endoctras. Hyatt, however, who 
at first adhered to Barrande s views on this question, came to the 
conclusion, after further study of the siphuncle of Aturia^ that the 
latter is related to the group of forms with short septal necks 
(Ellipochoanoida ^), in which the siphuncle is “ completed by an 
intervening connective wall of distinct structure from the septal 
funnels [necks]” 
Edwards^, adopting the opinion of von Bach, that the position of 
the sijjhuncle is of primary importance in the classification of fossil 
Cephalopods, united Aturia with Chjmeniam the family Clymenidae. 
But the involute shell and the unique form of the sutures in Aturia 
sufficiently distinguish it from Clymenia. Moreover, there are no 
fossils met with linking together these two genera in the course of 
the vast period of time that elapsed between the Devonian and the 
Eocene. Aturia cannot therefore be regarded as the descendant of 
Clymenia merely on account of the dorsal position and invaginated 
structure of its siphuncle. It can be shown, in fact, with some 
degree of probability, that these features did not possess the import- 
ance usually attached to them. Thus, in the type specimen of 
Nautilus [_Aturia'\ Parlcinsoni^ Edwards, there Is an ordinary cylin- 
drical siphuncle in a shell whose septal characters are distinctly 
those of an Aturia. The specimen in question is a fragment of a 
very large, most probably adult, shell (the height of the largest 
septum being about 9 inches), greatly surpassing in size any other 
shells hitherto assigned to Aturia. Hence one feels disposed to 
conclude that the funnel-shaped siphuncle ^ in Aturia was replaced 
by a simple one, when a certain stage in the growth of the shell 
had been attained. A large specimen of Aturia Parlinsoni from the 
London Clay (Lower Eocene) of Colchester tends rather to confirm 
this view of the case; that is, so far as may be judged from the 
somewhat imperfect view of the siphuncle in the youog shell, ob- 
tained by removing damaged portions of the outer whorl on one 
side of the specimen It must be admitted that the evidence 
’ This group embraces the Actinoceratidas and most of the true Nautiloids, 
including Nautilus. 
^ “ Genera of Foes. Ceph.,” Proceed. Boston Soc. Nat. Hist. vol. xxii. 1883, 
p. 271. 
Mon. Eocene Mollusea and Univalves of England, vol. i. 1849 (Mon. Pal. 
Soc.), p. 50. 
^ Using this term in its widest application to include the necks of the septa 
and their component parts. 
^ The latter operation was a difficult one owing to the tough and unyielding 
nature of the matrix (cement-stone) and the brittleness of the shell. 
