MODERN CLASSIFICATION. 



259 



Stoliczkaia argonautiformis, Stol. 



— crotaloides, Stol. 



— dispar, d'Orb. 



Stoliczkaia Telinga, Stol. 



— Rudra, Stol. 



— Xetra, Stol. 



Genus Crioceras, Leveille. — Shell discoidal, rolled on the same plane, whorls round, 

 spire regular, in all ages composed of turns of the cone disjoined and entirely separate. 

 Mouth round, oval, or compressed, formed by 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 wjiich larger ribs or rows of 

 tubercles are introduced at intervals ; as seen in Crioceras Emerici (fig. 177) the tubercles 

 are usually two smaller on the sides, and two larger and more thorn-like arising 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 symme- 

 trical 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 Duvalii, Leveille. The large Crioceras shells are found chiefly in the 

 Neocomian strata. I have collected Crioceras Boioerbankii, Sow., from the lower Green- 

 sand of Walpen and Ladder Chines, in the Atherfield section, Isle of Wight, many of 

 which were nearly two feet in diameter ; some forms are found in the Gault of France, and 

 the Speeton Clay of Yorkshire. This genus is limited to the Lower Cretaceous rocks. 



Fig. 177. — Crioceras Emerici, Leveille. 



Fig. 1 78. — Heferoceras Emerici, d'Orb. 



Genus Heteroceras, d'Orlig. — Shell spiral, turreted ; whorls in youth contiguous and 

 joined together; in age the last whorl separates itself from the others, and becomes (fig. 178) 

 produced and recurved, forming an arch without septa, which was doubtless the body- 

 chamber. Heteroceras is therefore a Turrilite with the body-chamber in age detached, 

 produced, and recurved. The most typical example is Heteroceras Emerici, d'Orb. 

 (fig. 178). 



