496 Miss Agnes Crane — Recent and Fossil Cephalopoda. 



but, it was not until the description by Professor Huxley ' of an 

 interesting fossil from the Ammonites ohtusus zone of the Lower 

 Lias, near Charmouth, in Dorset, in which the parts of the internal 

 structure known respectively as the pointed guard, the phragmocone, 

 or chambered portion, and the nacreous pro-ostracum were found 

 in situ with indications of an ink-bag, and tentacles armed with 

 horny hooks one-sixth of an inch long, that the anatomical details of 

 the genus Belemnites, as distinct from that of Belemnoteuthis, were 

 at length finally and satisfactorily established. 



So far, it is obvious, that there are two distinct types of Cephalo- 

 pods. One, with an external chambered shell, simply constructed 

 eyes, four gills, no suckers, and no ink-bag, very abundantly repre- 

 sented in the ancient seas, and those of the middle geologic epoch, 

 and of which one genus only survives at the present day. The 

 other, possessing an internal shell, two gills, tentacles armed with 

 suckers, and sometimes hooks, an ink-bag, and perfect organs of 

 vision, appeared first in the Triassic period, was largely developed 

 in the Jurassic seas, and predominates in the existing oceans. 

 When the ancient tetrabranchs were the rulers of the seas during 

 the " reign of Molluscs," the Gasteropodous class was represented 

 chiefly by the lowest organized herbivorous forms, the carnivorous 

 snails, etc., not making their appearance until the Secondary epoch, 

 when they became the contemporaries of the dibranchiate Cephalo- 

 pods. In past ages the Tetrabranchs probably performed the office 

 of restricting the undue increase of the co-existing Crustaceans and 

 Mollusca, and possibly their own numerical abundance was in turn 

 influenced by the appearance and development in Devonian and 

 Carboniferous times of the formidable armour-plated fishes. In the 

 Secondary period, the dibranchiates served as food for the extinct 

 Enaliosaurians, or Sea-lizards, as in the present day, for the pre- 

 dacious fishes, penguins, and other sea-birds, some species of cetacea, 

 and, in a few countries, even for man.^ Thus, both groups fulfilled 

 their functions in the economy of nature, and the balance of power 

 was maintained. Of all the vast families of Naiitilidce, Goniatidce, 

 and Ammonitidce, the long-lived Nautilvs alone survives. "Whether 

 the increase of the more highly organized group affected the further 

 development of the lower forms, cannot positively be affirmed ; but 

 it is certain that the causes which led to the extinction of the 

 Tetrahrancliiates (with the exception aforesaid), at the close of the 

 Cretaceous epoch, had no influence whatever vipon the more highly 

 organized forms, which persisted through the Tertiaries, and abound 

 in the existing oceans. 



There remains but to consider the evidence of the Cephalopods 

 with regard to the theory of Evolution, a subject on which opinions 

 are naturally very diverse. The existence of a certain amount of 



1 Mem. Geological Survey, Monograph II., 1864. 



2 Octopods, cuttles, and squids were highly esteemed as epicurean dainties in 

 ancient Eome, and the former are now largely consumed as food in the sea-coast 

 towns of France and Italy. "While according to Dr. Macdonald the Pearly Nautilus 

 is regarded as an agreeahle viand by the inhabitants of the Feejee Islands ! 



