568 MOLLUSCA SUB-KINGDOM VI 
D. (Phyl.) rakosense, Herbich sp.; Schistophylloceras, gen. nov. Type S. (Phyl.) 
aulonotum, Herbich sp.; Geyeroceras, gen. noy. Type G. (Phyll.) cylindricum, Geyer 
sp.; Tragophylloceras, gen. nov. Type T. (Phyl.) heterophyllus-nwmismalis, Quenst. 
sp.; Meneghiniceras, gen. nov. Type M. (Phyl.) lariense, Menegh. sp. Trias to 
Cretaceous. , 
Sub-Order H. LEPTOCAMPYLI. Hyatt. 
Shells with peculiar, more or less crenulated ornamentation, due to the intersection of 
two systems of lines, transverse bands of growth, and longitudinal creases and ridges, 
sometimes developing into spines. Aspect more discoidal and larval, and with fewer 
highly involute forms than in other sub-orders. Shell often constricted as in Phyllo- 
campyli. Characterised in some families by the small number of completely developed 
lobes and saddles. Outlines of sutwres extremely complex, and saddles generally much 
reduced owing to excessive development of the lobes. 
The antisiphonal lobe has in most families a cruciform aspect, due to the develop- 
ment of a large pair of branching marginal lobes. In the Lytoceratidae there is also 
an inward growth of the two marginals near the tips, so that they rest upon the oral 
surfaces of the septa instead of against the inner surface of the dorsum; these modi- 
fications being peculiar to this sub-order. The principal inflections are more 
numerous in the young, and reduction takes place in later stages through arrested 
development and suppression of those nearest the lines of involution. Wiahner’s 
thorough researches have shown the close affinities of Plewracanthites with Psiloceras 
and Caloceras, which lie at the ancestral base of this sub-order. This accounts for the 
similarities between the young of this group and Phylloceratidae, as demonstrated by 
J. P. Smith. A number of phylogerontic uncoiled genera occur in the Cretaceous. 
Family 1. Pleuracanthitidae. Discoidal, plicated, or costated shells, having 
crescentic tubercles or hollow spines in some species ;, venter rounded except in extreme 
age of a few species, in which a faint keel appears. Aperture has a short rostrum 
with deep ventro-lateral 
or lateral sinuses, and 
lateral or dorso - lateral 
crests. 
Pleuracanthites, Cana- 
vari; Analytoceras, gen. 
nov. Type A. (ag) 
articulatum, Wilner sp. 
Lias. 
Family 2. Tetra- 
gonitidae. Smooth, 
discoidal, and  involute 
shells, with flattened or 
rounded venter, and more 
or less flattened sides, 
Constrictions and spines 
sometimes present. Sutures 
sometimes reduced to four 
paired saddles and three 
lobes on the dorsum, or 
there may be only two 
pairs, or a single pair of 
large saddles. Siphonal lobes deeper and broader than in Lytoceratidae, the siphonal 
saddles larger, and laterals more numerous, comprising sometimes as many as nine pairs of 
complex zygous lobes and saddles. Antisiphonal lobe straight, complex, trifid, or bifid. 

Pia. 1175. 
Haploceras elimatum, Oppel sp. Tithonian ; Stramberg, Moravia. 
