530 TRANSACTIONS OF SECTION D. 
Professor Jaekel (19), formerly of Berlin, now of Greifswald, the author of the 
memoir referred to, lays down a number of theses regarding the organisation and 
mode of life of these extinct species, and I venture to give an abstract of his views, 
premising that my acquaintance with paleontology does not justify me in expressing 
a definite opinion as to the validity of his conclusions, though they seem extremely 
reasonable, 
His opening statement is that Orthoceras and its allies were not free-swimming 
but sessile organisms, and this is based on the following arguments amongst 
others. The shells were thicker and heavier than any that are found in pelagic 
organisms; the external sculpture shows that the shell was not embedded in the 
soft parts, and if it were exposed the annulate arrangement of many forms is incon- 
sistent with their easy passage through the water; the ‘lines’ (in the naval 
architect’s sense of the word) of an organism intended for navigation are always 
smooth and not wavy; otherwise undue friction against the water would be 
created ; whilst the straight transverse margin of the aperture of the shell shows 
that it was not carried by a creeping body like that ofa snail. Their sessile nature 
is further shown in the first place by the radial symmetry, which is rare in free- 
swimming forms, and almost unknown in those whose axis is long in proportion to 
their diameter. Further, the termination of the shell is generally broken off: of 
all the thousands of specimens which have been examined, but very few show the 
initial chamber ; in those cases in which the apex is preserved it shows a scar, 
where the siphuncle entered the protoconch, The separation of the shell into 
chambers by transverse septa occurs only in sessile forms, but in such it is found 
in many divisions of the animal kingdom; for example, Corals, Cheetetidee (among 
Polyzoa), Hippurites and Vermetus (among Mollusca), and Richthofenia (among 
Brachiopoda?). The reason of this cameration is to be found in a constant effort to 
keep the body of the animal above the surface of the mud in which it is rooted. 
On this view the siphuncle admits of a simple explanation; it is the vestigial part 
of the body which has been contracted and partially cut off as the body has moved 
successively forward to the enlarged superior portion of the shell. In harmony 
with this is the fact that the siphuncle is wider in the more primitive forms; the 
name ‘siphuncle’ on this theory is rather a misnomer, for it is not in the usual 
sense of the word a ‘siphon.’ The expansion of the siphuncle in the chambers is 
explained by the need for diminishing the air spaces so as to increase the weight 
and consequent stability of the organism. 
The fossils known as Conularia were probably a primitive form of the same 
kind, and possibly even belong to the ancestral line of the Cephalopoda. They 
were conical shells of chitin or conchiolin, radially symmetrical with internal 
transverse septa, and are commonly found broken off at the apex. A recent obser- 
vation of Ruedemann (38) has shown that they are sessile, a group of them 
branching out from a common support. It may be added that J. M. Clarke (9) 
has recorded a case in the American Upper Devonian rocks in which the majority 
of the large Orthoceratidee were fossilised in a vertical or but slightly sloping 
osition. 
. According to this view the coiled Nautilide were free-living forms like the 
Nautilus of to-day, and were probably free from the outset, for they could scarcely 
have been derived by gradual bending from astraight Orthoceras. The half-coiled 
forms have been derived from the coiled, not from the straight. The forms such as 
Phragmoceras, &c., in which the aperture of the shell is contracted, and often shows 
bilaterally symmetrical notches, are interpreted as having lived buried in the mud. 
The notches served for the protrusion of the arms, vent, and siphon, which latter 
were probably elongated tubes stretching up through apertures excavated in the 
mud, much in the same way as the heart-urchin (Zchinocardium) among the sea- 
urchins lives buried in the mud, and obtains nourishment by stretching its tube 
feet up to its surface. The arrangement of the arms was probably like that seen 
in the embryos of Dibranchiata, or of the circumoral appendages of Nautilus. 
Turning to the extensive and interesting group of Belemnites, Professor Jaekel 
enunciates the view that these were not, as has been commonly believed, active free- 
swimming forms, the rostrum (guard serving as the pointed ram of a battleship, 
