ORDER II AMMONOIDEA 547 
TABLE SHOWING PRINCIPAL DIVISIONS OF THE AMMONOIDEA. 
New Sus-OrpDEks. EQUIVALENTS UNDER FoRMER SYSTEMS. 
Clymenia, Clymenidae (Clymenioids). 
Intra- { 
siphonata Gastrocampyli il. , ; 
# 2 rasirocampy Characters same as sub-order. Devonian. 
Zatbels: > \ 
( 
Microcampyli 
it 
a 
Goniatites, Goniatitidae (Goniatitoids). 
Zygous inflections entire only in simple or radical 
forms, becoming divided and similar to Ceratitoids only 

Mesocampyli ; 3 Se 2 : 
BY U j in some highly specialised genera of the Permian and 
Danae * | Trias. The young are asellate in radical forms, becoming 
ee latisellate in more specialised genera. Mostly Devonian 
Glossocampyli 

and Carboniferous ; comparatively few Permian repre- 
Lsentatives. 
( Ceratites, Ceratitidae (Ceratitoids). 
| Zygous inflections entire only in a few radical forms, 
probably derived from the same radicals as the Phyllo- 
campyli. Lobes become divided by fine marginals 
forming serrations, but bases of saddles remain entire 
except in highly specialised genera. Supposed to be 
mostly latisellate, becoming angustisellate in specialised 
forms. ‘Triassic. 

Extra- 
siphonata, 
Discocampyli III. 4 
Zittel. | 
Zygous inflections entire only in Palaeozoic radicals of 
Phyllocampyli the Phyllocampyli. Lobes become divided by fewer and 
Leptocampyli larger marginals than in Ceratitoids ; bases of saddles 
IV. {remain entire only in simpler forms of the Triassic 
Pachyecaimpyli Phyllocampyli. All others have completely divided 
inflections except some of the degraded Pachycampyli. 
Phyllocampyli range from Devonian to Cretaceous. The 
I 5 site ees 
| ( Ammonites, Ammonitidae (Ammonitoids). 
L (last two sub-orders are Jurassic and Cretaceous. 
Sub-Order A. GASTROCAMPYLI. Hyatt. 
Conchs varying from forms like Anarcestes to those that are more or less compressed in 
section, and from completely discoidal to compressed and highly involute shells, the surface 
being either smooth or with large spines. The characteristic ventral saddles are almost 
imperceptible in some primitive species, and although entire and large as a rule, are in 
some genera divided by entire ventral lobes.  Septa concave along the mesal plane. 
Siphuncle dorsally situated. Living chamber occupying about three-fourths of a volution ; 
aperture with hypononie sinus. 
The ventral saddles are developed by the obliteration of primitive ventral lobes 
and fusion of the first pair of saddles (Branco). It is at present questionable whether 
the ventral lobes of some genera are secondary modifications or retentions of the 
primitive ventrals, and also whether these can be regarded as divided ventrals even in 
the Cymaclymenidae. The antisiphonal lobe is large and long, and often fused with 
the siphuncular funnels, which are long and single (monochoanitic). The dorsal sutures, 
so far as known, are very peculiar, having only a pair of large saddles confluent with 
the last pair of external saddles ; or one pair of zygous saddles, and one pair of zygous 
lobes, the second pair of zygous saddles being confluent with the innermost external pair. 
The perforation through the umbilicus, so constant in Nautiloids, is absent, and so 
too are the umbilical depressions on either side of the neck of the protoconch, common 
in other Ammonoids. The forms are nevertheless ammoniticones, having the proto- 
conch and other characters of the order. The first septum is described as asellate 
(Branco), but figured as having a broad saddle on the venter. 
Family 1. Clymenidae. Giimbel (emend). Primitive forms similar to Anar- 
