574 MOLLUSCA SUB-KINGDOM VI 
the sutures acquire phylliform marginals like those of Phyllocampyli; but this is not in- 
variably the case, and characters of the dorsal and 
lateral sutures as well as of the shell vary in different 
directions. In one direction they join with Caloceras 
at the base of the present sub-order ; in another they 
unite with Angulatida, as recognised by most observers ; 
and in a third they show affinities with Agassiceras. 
Psiloceras, Hyatt (Fig. 1194); Parapsiloceras, 
gen. nov. Type P. (Psil.) calliphyllum, var. poly- 
eyclum, Wihner. Lower Lias. 
II. ANGULATIDA. 
Primitive discoidal shells indicate probable union 
with Psiloceras, but tend to evolve forms in which the 
venter is smooth, channeled, or crossed by costae at 
some stage of growth even when keeled. Lateral 
sutures more complex than in Arietida, and apt to be 
inclined apicad in specialised shells; dorsal sutwres 
like those of Arietida. 
Family 2. Angulatidae. More or less com- 
pressed and costated shells, the costae sometimes 
crossing the venter in the young or extreme age, but usually interrupted in the adult 
by a smooth and occasionally sunken median zone. Sutures inclined apicad near 
lines of involution, more complex in outline 
than in typical Arietidae, and with phylliform 
marginals more like those of Pstloceras. 
Ventral lobe broader and shorter, with larger 
siphonal saddles than <Arvetidae, and anti- 
siphonal lobe bifid, longer, and more complex. 
First pair of dorsal saddles large and long, 
other dorsal inflections variable, but generally 
more numerous than in Arietidae. 
Schlotheimia, Bayle (Fig. 1195); Vaehnero- 
ceras, Hyatt. Lower Lias. 
Family 3. Polymorphidae. Haug. 
Shells compressed discoidal, with smooth young 
like those of Psiloceras. Costae apt to be in- 
clined or slightly sigmoidal, and continuous 
across the venter, This iscrenulated in primi- | . : ; 
tive forms, but becomes smooth, channeled, or Ge eee ee a 
keeled in specialised shells. The latter have 
sutures similar to those of Angulatidae and Liparoceratidae, Wut less complex. Connects 
with Psiloceras through Gemmelaroceras. 
Polymorphites, Sutner; Amphiceras, Gemm.; Uptonia, Tmetoceras, Buckm, ; 
Gemmellaroceras, gen. nov. Type G. (Aegoc.) aenigmatum, Gemm. sp. . Lias and 
Inferior Oolite. 

Fic. 1194. 
Psiloceras planorbis, Sowb. sp. Infra- 
Lias; Bebenhausen, Wiirtemberg. Ana- 
ptychus in living chamber. 

Fic. 1195. 
III. ARrerrpa. 
Primitive discoidal forms keeled and often channeled, with sides costated as in Coro- 
niceras, etc. Euternal sutures limited, as a rule, and auxiliaries rise orad toward lines 
of involution, but may be considerably extended, and number of inflections increased in 
highly involute shells. Dorsal sutures still more limited, and never have the monophyllic 
ee 
