228 TESTACEOUS CEPHALOPODS. 



have farther evidence to show^, that in times anterior to, and 

 during the deposition of the Chalk, the same important func- 

 tions v^^ere consigned to other carnivorous Mollusks, viz. the 

 Testaceous Cephalopods ;* these are of comparatively rare 

 occurrence in the Tertiary strata, and in our modern seas ; 

 but, throughout the Secondary and Transition formations, 

 where carnivorous Trachelipods are either w^holly wanting, 

 or extremely scarce, we find abundant remains of carnivo- 

 rous Cephalopods, consisting of the chambered shells of Nau- 

 tili and Ammonites, and many kindred extinct genera of 

 polythalamous shells of extraordinary beauty. The Mollus- 

 cous inhabitants of all these chambered shells, probably pos- 

 sessed the voracious habits of the modern Cuttle Fish, and 

 by feeding like them upon young Testacea and Crustacea, 

 restricted the excessive increase of animal life at the bottom 

 of the more ancient seas. Their sudden and nearly total 

 disappearance at the commencement of the Tertiary era, 

 would have caused a blank in the " police of nature," allow- 

 ing the herbivorous tribes to increase to an excess, that 

 would ultimately have been destructive of marine vegeta- 

 tion, as well as of themselves, had they not been replaced 

 by a different order of carnivorous creatures, destined to 

 perform in another manner, the office which the inhabitants 

 of Ammonites and various extinct genera of chambered 

 shells then ceased to discharge. From that time onwards, 

 we have evidence of the abundance of carnivorous Trache- 

 lipodes, and we see good reason to adopt the conclusion of 

 Mr. Dillwyn, that " in the formations above the Chalk, the 

 vast and sudden decrease of one predaceous tribe has been 

 provided for by the creation of many new genera, and 

 species, possessed of similar appetencies, and yet formed for 

 obtaining their prey by habits entirely difterent from those 

 of the Cephalopods. "f 



* See explanation of the term Cephalopod, in note at p. 230. 



t Mr. Dillwyn observes farther, that all the herbivorous marine Cepha- 



