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Genus Criocreras, Léveillé.—Shell discoidal rolled on the same 
plane, whorls round, spine regular, in all ages composed of turns 
of the cone, which are disjoined and entirely separate. Mouth 
round, oval, or compressed, forming a slight thickening of the 
inner lamina of the shell. Body-chamber about two thirds the 
length of a whorl. 
The sculpture consists of small encircling ribs, among which 
larger ribs or rows of tubercles are introduced at intervals 
(fig. 78). As seen in Crioceras Emerici the tubercles are usually 
two smaller on the sides, and two larger and more thorn-like 
arise from the border of the siphonal area, the disjunction of 
the whorls extends up to first formed coil. The lobe-line is 
highly ramified, and consists of a large siphonal lobe, with long 
symmetrical branches, a principal lateral on each side, with 
long, wide, spreading digitations, which are nearly but not 
quite symmetrical, a lower lateral on each side, much smaller 
than the principal, and a columellar lobe which is well developed. 
Such is the structure of the lobes in Crioceras Duvalli, Liveries. 
The large Crioceras shells are found chiefly in the Neocomian 
strata. I have collected Crioceras Bowerbankii, Sow., from the 
lower Greensand, in the Walpen and Ladder Sands of the 
Atherfield section, Isle of Wight, some of which were nearly two 
feet in diameter; some forms are found in the Gault of France, 
and the Speeton clay of Yorkshire, so that this genus is limited 
to the lower Cretaceous rocks. 
Fic. 79.—Crioceras Emerici, Léveille. Fic. 80.—Heteroceras Emerici, d’Orb. 
