87O TETRABRANCHIATE CEPHALOPODS. 



Also very closely allied to Crioceras, if not absolutely identical 

 with it, is the genus Ancyloceras (fig. 803), in which the shell agrees 

 with that of the former in consisting in its earlier portion of several 

 volutions, which are coiled into a flat spiral, but are not in contact 

 with one another. The shell differs, however, from that of Crioceras 

 in the fact that the last volution is produced at a tangent, and is 

 ultimately bent back in the form of a crosier. The sutures are 

 divided into six lobes, which are very unequal in size, and are 

 digitated in a complex manner. The genus is Jurassic and Creta- 

 ceous, ranging from the Inferior Oolite to the Neocomian. 



