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Genus Herrroceras, d’Orb.—Shell spiral turreted, whorls in 
growth contiguous and joined together in age, the last whorl 
separates itself from the others and becomes (fig. 80,) produced 
and re-curved, forming an arch with septa, and which was 
doubtless the body-chamber. Heteroceras is therefore a tur- 
rilite, with the body in age detached, produced, and re-curved. - 
The most typical example is Heteroceras Emerici, v’Orp, fig. 80. 
Genus 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 having stronger ribs at intervals 
developed. The sculpture consists of two rows of tubercles 
developed upon each side of the large ribs, and two rows of 
larger tubercles on the borders of the siphonal area, as shown 
in Toxoceras Honnoratianum, fig.81. 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 is symmetrical, the stem is short, 
and the bifurcate branches are long; the superior lateral is 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, is found in the lower 
stages of the Cretaceous rocks; all the larger specimens are 
obtained from the lower and upper N eocomian strata. 
-Fia. 81.—Toxoceras Honnoratianum, a'Orb. Fic. 82.—Aspidoceras longi- 
spinum, Sow. 
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