260 
THE LIAS AMMONITES. 
Gemis ToxocERAS, d' Orb. — Shell conical, subcylindrical, or compressed, symmetrical, 
elongated, more or less arched, but never forming a spiral. Sides of the shell ornamented 
with encircling ribs ; in some forms stronger ribs are developed at intervals. Or the 
sculpture consists of two rows of tubercles which grow upon each side of the large ribs, and 
two rows of larger tubercles on the borders of the siphonal area, as shown in Toxoceras 
Honnoratianiim (fig. 179). The mouth is round, oval, or compressed, with a prominent 
internal border, and the large ribs on the sides and ventral surfaces represent the different 
stages of growth of this bent cone. The lobe-line is very much ramified ; the siphonal 
lobe symmetrical, the stem short, and the bifurcate branches long ; the superior lateral 
very large and composed of nearly symmetrical branches ; the lower lateral is small, the 
columellar lobe has considerable dimensions, and is nearly symmetrical in its structure. 
The affinities of this genus, regarding the structure of its lobes, is with the preceding genus 
Crioceras ; and, like it, it is found in the lower stages of the Cretaceous rocks ; all the 
larger specimens are obtained from the lower and upper Neocomian strata. 
Fig. 179. — Toxoceras Honnoratianum, d'Orb. Fig. 180. — Aspidoceras longispinum, Sow. 
Genus Aspidoceras, Zittel. — The form of the shell in this genus is very variable. 
Sometimes it is flat and discoidal with a wide umbilicus, or large, inflated, and 
highly involute. The siphonal or ventral area is rounded or flattened, the sides are 
adorned with fine ribs, and the sculpture consists of two rows of tubercles developed at 
intervals among the finer folds o£ the shell in its early age, which seem to disappear 
or are undeveloped in later years. The lobe-line ramifications are simple in Aspid. 
perarmatum, Sow. The siphonal lobe is large with symmetrical branches, the principal 
lateral is large and composed of numerous unequal parts, and the lower lateral is much 
smaller. The body of the lobes and saddles is broad, and the lobes are much slit up 
into branches. Aspid. longispinum. Sow. (fig. 180), from the Oxfordian of Weymouth, 
has a thick, discoidal, smooth shell, with two concentric rows of short spines growing upon 
the sides of the whorls, which are few and more than one half involute. This forms a 
very good type of the group. The large section of the Perarniati, with a double ro\v of 
tubercles on the sides of the whorls, appears to want auxiliary lobes. In the group 
which has Aspid. Altenense, d'Orb., from the Corallian, for its type, one row- of tubercles 
