AMMONITES. 357 



bosses, variously disposed in the different species, for the purpose 

 of strengthening them. In the species represented in the accom- 

 panying figure, these ribs are very prominent. The curiously 

 complicated septa or partitions of the chambers also assisted in 

 strengthening these large shells. 



FIG. 650. AMMONIT 



970. Several kinds of chambered shells, with sinuous parti- 

 tions, are met with in various strata. These seern to have borne 

 the same relation to the Ammonite, as the Orthoceratite to the 

 Nautilus; and they have been arranged according to their 

 minuter diversities of structure. Some of them are spirally 

 curved, but the several whorls or turns of the spire are not in 

 contact with each other ; this is the case with the Crioceratite. 

 Others are straight, or but slightly curved ; such as the Baculite. 

 The Turrilite, again, has more of a corkscrew curve, resembling 

 that of many Gasteropod shells. There is good reason to believe 

 that this group, which most abounded* at the period when the 

 Ichthyosaurus and Plesiosaurus were the principal inhabitants of 

 the sea and shores, was preyed on by these marine tyrants ; the 

 remains of the beaks, and even of the horny rings surrounding 

 the suckers, of Cephalopods, having been found in the fossilized 

 excrement of those Reptiles. 



VOL. II. C C 



