538 MOLLUSCA SUB-KINGDOM VI 
septum closed the aperture of the protoconch, and the caecum projected into 
its interior. The caecum is connected with the internal surface of the proto- 
conch by bands (Figs. 1101, 1102), or semiconical prolongations, described 
by Munier-Chalmas as the prosiphon. But 
these bands are of various shapes, are not 
connected with the interior of the caecum, 
and appear to be merely calcareous supports 
for the bottom of the caecum. The earliest 
sutures, described in a masterly way by 
Branco, are divided by him into three classes : 
Fie. 1091. asellate, latisellate, and angustisellate (Figs. 
phyllom Sow tp. Paes. | Nivoceras heiero- 1089-1091). The first cross the venter as a 
straight line or very slight saddle, and are 
present only in the ephebic stages of Cyrtoclymenia(?) and in the mimoceran 
stage of the Microcampyli. In all except primitive forms it is confined (as are 
most of the purely nautiloidean characters) to the first septum. The latisellate 
stage is characterised by a decided broad saddle on the venter, with corre- 
sponding deeper and broader lobes on the sides. The angustisellate stage has 
prominent, sometimes almost sub-acute ventral saddles with corresponding deep 
lateral lobes, accompanied by definite saddles at the umbilical depressions. 
The last two stages are progressive modifications confined to the larvae of 
Ammonoids, and are not present in the ephebie stages of any known species. 
The asellate condition of the first septum is found in the ananepionic stage of 
one species of the Gastrocampyli, according to Branco, but his figure shows a 
saddle on the venter. The Microcampyli and Mesocampyli are asellate, and the 
ELurycampyli also in 
some primitive De- 
vonian genera, but 
latisellate in others, 
and angustisellate 
in the Trias. The 
embryos of primi- 
tive Phyllocampyli 
are unknown, but 
the Triassic Lobi- 
tidae and Arcestidae 
are latisellate, while Fic. 1092. 
the Cladiscitidae and a Development of sutures in a latisellate Goniatite (Glyphioceras diadema, 
5 Goldf. sp.). Carboniferous Limestone ; Choquier, Belgium. , Same in a latisel- 
2 lh is es q 
the Phylloceratidae late Ammonite (Tropites subbullatus, Hauer). C, Same in ‘an angustisellate 
S ‘ ape : Ammonite (all after Branco). Sutures of the first volution are lettered con- 
o 
are angustisellate secutively from g to 1; those of the second from m to s. 8 
throughout. The 
embryos of Discocampyli are almost unknown, but are supposed to be latisellate, 
with the exception of the highly specialised Pinacoceratidae, which are angusti- 
sellate. The remaining sub-orders are wholly Jurassic and Cretaceous, and so 
far as known, the first septa are angustisellate. 
Sutures.'—The second septum (Fig. 1092) in all but the most primitive 
A B 
A B C 


' [The nomenclature commonly in vogue designates the sutural inflections as follows :—The ventral 
or external lobe is bounded on either side of the mesal plane by the large jirst or superior-lateral 
saddle. This is followed by the first or superior-lateral lobe, and then come the second or inferior- 
lateral saddle and lobe in the order named. All additional inflections occurring between the second 
