2o8 The American Geologist. ^p"'- i^°^- 
etc] the shell parts approaching each other above the funnel 
leave a slit open between them. Its inception in all dibranch- 
iates argues for the secondary coalescence of the walls. There 
is on the whole little probability (hat a funnel like that of Nau- 
tilus was placed under this slit; we will hardly be amiss if we 
locate the arms in the aperture which is directed aborally back- 
ward. The funnel in the typical form of a folded muscle-plate, 
as it is found persistently in Nautilus and embryonally in the 
dibranchiates, or in the specialized form of a distally circular, 
coalescent tube, as in the mature dibranchiates, presents prob- 
ably specialized conditions adapted to the peculiar mode of 
movement of free living cephalopods. I consider it probable 
that the arms of these older nautiloids were spread out blade- 
like and, as in Nautilus, provided with erectile tentacles. The 
contracted aperture of several ammonites appears so similar to 
that of the gomphoceratites, that one may at least infer blade- 
or spathe-like arms. . . . 
"The activity of these formis can hardly have been very 
great or comparable in any way to that of recent dibranchiates. 
The advanced closure of the shell suggests the balanides and 
lepadides, the bryozoans and various types of worms as serpu- 
lites, and seems, therefore to suggest the probability that these 
for genera mentioned (Hexameroceras etc.) were sessile. -The 
manner in which the shell conformed itself to the arm-bases 
appears most easily explained as a special provision for pre- 
venting -an intrusion of foreign bodies between mantle and 
shell. This fact, pointing tO' a strong dependence upon the 
bottom, together with the bilaterally symmetric form of tlie 
shell, has led me tO' the supposition that these animals lay im- 
bedded vertically (hence symmetrically) in the bottom of the 
sea and spread out their arms upon it. The strong projection 
of the funnel-sinus would also be explained by this supposition, 
as it then would have had to exercise the function of a real 
siphuncle. To colleagues, to whom this explanation may ap- 
pear strange and bold, I wish to point out that some Spatan- 
gidse lie buried about a foot deep in the sea bottom, protrude 
their long tentacles through a tube, and through another dis- 
charge, by energetic water current, the contents of their intes- 
tine. Here one has, therefore, quite analogous conditions, 
which would have hardly been expected from an cchinid. 
