NOMENCLATURE OF STAGES OF GROWTH AND DECLINE, 11 
It is obvious that we cannot ac- 
count for the nautilus-like ven- 
tral saddle of the earlier sutures 
of the Ammonoids, the calca- 
reous shell of the protoconch, 
the coecal stage, the absence of 
the collar in the lower Goniati- 
tine and in the young of the 
higher forms, the often central 
position of the siphon in the 
young, and many other charac- 
ters, unless we admit a proba- 
ble derivation of the Goniatitinee 
from some straight microsipho- 
nulate form of Nautiloid. It is, 
therefore, highly probable that 
the pteropod-like aspect of the 
young of some Goniatitinas may 
be a purely homoplastic charac- 
ter, and be meaningless so far as 
the genesis of the group is con- 
cerned. 
7. The next or second of the 
neepionic stages was represented 
by a living chamber, which was 
completed by the building of the 
first septum with its attached 
cecum, indicating the primitive 
beginnings of a siphon. This 
stage we styled the Czcosipho- 
nula, and we have considered the 
possession of a cacum to be an 
indication of the former exist- 
ence of an ancestor having a 
central series of cecal pouches. 
These may have had functional 
communication in some forms by 
means of an endosiphon, as in 
the Endoceratide, and in others, 
either belonging to this family or 
to a more primitive group, they 
may have been closed cxca. 
8. The next nepionic stage 
was ended when the second sep- 
tum was built in the modern 
Fig. 9,10. Views from the side and below of the plug which the 
animal of Orth. uncatum, Barr., habitually built on the exterior 
of the broken or truncated end of its shell. The last suture 
is shown in Fig. 9, and the internal shadowy markings are 
apparent in both figures at a, g. These, however, in Fig. 9, 
are too far removed from the exterior. When the outer layer 
of the plug is penetrated, they are seen to be a part of its 
structure. ‘The side view is also defective in the drawing of 
the pseudo siphon (d). There should be three distinct steps 
indicating three layers. ‘The external crenulated strie of the 
plug appear at h. Loc. Bohemia, Coll. British Museum. 
1 2. Views of the same from the side and below, to show 
the external markings of the plug (h), which contrast strongly 
with the perfectly smooth shell above the septum of trunca- 
tion and internal strie (1) which appear when the. outer layer 
is fractured. No septa ever occur in the plugs. These figures 
are introduced in order to meet M. Barrande’s objections (Syst. 
Syl. Pl. 488), that the examples of what we have called the 
protoconch and apex of the true conch were in reality plugs 
similar to those of Orth. truncatum. There is no need of mak- 
ing any remarks; if our figures are correct, we are right in 
our statements. It may, however, be well in this connection 
to say that M. Barrande has done us the honor to make use of 
a number of our figures, including in part the above. 
Fig. 13-15. Views of the cicatrix and apex of Orth, unguis, Phill., 
after the shedding or remoyal of the protoconch as it usually 
occurs, leaving the cicatrix uninjured. Fig. 13 shows the area 
of the cicatrix much enlarged; b, conch or apex forming a 
smooth shoulder; and ec, depressed surface of the cicatrix. 
Fig. 14, view less magnified of apex; Fig. 15, section of same. 
Loe. Dublin, Coll. British Museum. 
Fig. 16. Apex of Orth. unguis, Phill. natural size, with first three 
sutures. 
Fig. 17. Apex of same species after the probably violent removal 
of the protoconch, showing the fractured shell (b), and the 
unusual aspect of the cicatrix. ‘This and Fig. 16 are types. 
Loc. Yorkshire, Coll. British Museum. 
Fig. 18. Front view of Fig. 19. The broken line (k) is hy potheti- 
cal. It indicates the possible outline and position of the caecum, 
supposing the oval area in the centre of Fig. 19 to have repre- 
sented that organ. 
Fig. 19. Apex of Orth. politum from below. The protoconch has also 
been violently removed, and the opening plugged, apparently 
from within. The dark spot on the right seemed to be a rup- 
ture in the external surface. The oval shade in the centre indi- 
cated an internal structure, which may have been the caecum In 
the first air-chamber. Loc. St. Cassian, Coll. British Museum. 
