ORDER II AMMONOIDEA 537 
and no perforation is visible even under a magnifier. There are two pits, 
however, one on either side of the apical end of the conch, which remain as 
remnants of this perforation, and are present in all ammoniticones (except 
perhaps certain G'astrocampyli). The bactriticone obviously represents the 
primitive or primary radical of the Ammonoidea, and the mimoceracone the 
next or secondary radical of this order. 
Ammoniticones of the MJicrocampyli introduce a peculiar form of volution, 
the anarcestean (Fig. 1122), which is depressed and crescentic in section, and 
may be regarded as the Tertiary radical. These forms evolve a series becoming 
more involute and compressed (Fig. 1123), and some with elevated or narrow 
venters and well-defined lateral zones (Fig. 1124), but still retaining in the 
young more or less of the anarcestean aspect. The Castrocampyli have a few 
radical forms of similar aspect and with somewhat similar sutures (Fig. 1116) ; 
they then produce a series of compressed discoidal shells having cordiform or 
quadrate sections (Figs. 1117-1119), and these also develop involute forms 
among specialised species. The Mesocampyli and Glossocampyli have a similar 
history, but in the Hurycampyli coronate or gastrioceran forms (representing a 
quaternary radical) with trapezoidal section and broad venter become common 
in the ephebic stages (Fig. 1132). The primitive radical forms of the 
anarcestean ammoniticones are replaced among the Phyllocampyli by the 
smooth, discoidal, compressed quinary radical, or prolecanitean type (Fig. 1155). 
This appears among the adult Gastrocampyli, although with distinct sutures, 
and is also found among the Discocampyli. In the more specialised sub-orders, 
the anarcestean type reappears only during the young stages. These last two 

A B 
A 
Fic. 1089. 
Asellate protoconch of Gephyroceras caleuli- Big: 1090: 
forme, Beyr. sp. Upper Devonian ; Biidesheim, Latisellate stage of Arcestes cymbiformis, Wulfen sp. 
Eifel. A, Viewed from in front. B, From the Trias; Aussee, Austria. A, Viewed from in front. 
side (after Branco). B, From the side (after Branco). 
radicals persist into the Jura and Cretaceous, but exhibit more complex sutures 
and other progressive structural changes in their ephebic stages. . 
Phylogerontic series (2habdoceras, Cochloceras) make their appearance in the 
Upper Trias, become more abundant in the Jura, and still more important 
during the Cretaceous. They have their own peculiar radicals, sometimes 
found among discoidal and again among more involute shells, but for the 
most part they do not originate from smooth shells. 
The same descriptive terms are used for shell characters among Ammonoids 
as among Nautiloids (see p. 512 ef seq.). Obviously the first stage of the 
conch was that of a living chamber, the protoconch being without internal 
septa or siphuncle (Fig. 1101). Then, after building out the usually flattened 
neck or apical part of the conch, the animal rested, and the first septum as 
well as the caecwm (or incipient stage of the siphuncle) was secreted. The first 
