80 PALEONTOLOGY 



finally extinct only in the last century, owing to the destruction 

 of the native woods by the instrumentality of goats and swine. 

 Tcctibranchiata. — The families typified by Twnatdla,Ringi- 

 cula, and Bulla played a more important part in the secondary 

 and tertiary periods, but their affinities have been seldom un- 

 derstood. The cone-like Adconina appeared in the carbonifer- 

 ous rocks, and attained a remarkable development in the lias 

 (fig. 18, 10). They were succeeded by the Adeondkv, with a 

 plaited columella, in the cretaceous strata; and by Volvaria 

 (fig. 19, n) in the eocene. The diminutive Ringiculce of our 

 seas were preceded by large species of the same genus in the 

 tertiaries, and by Cinulia (fig. 18, 9), Globicondia, and Tylo- 

 stoma, in the cretaceous strata. The genus Varigcra has varices 

 recurring twice in each whirl, like Ev.lima ; and Ptcrodonta 

 is winged like Strovibus. 



Class IV.— CEPHALOPODA. 



Order 1. — Tetrabranchiata. 



(Nautiloid Cephalopoda.) 



Of the lower group of Cephalopods, possessing chambered 

 shells similar to the pearly Nautili, there are 1400 extinct 

 species, belonging to above 30 genera, while 3 or 4 species 

 alone exist in modern seas. These fossils resemble the Nauti- 

 lus, and differ from the dibranchiate Spirula in the structure 

 of their shell, which is composed of two layers, the outer por- 

 cellanous, the inner pearly ; whereas the Sjnrula — an internal 

 shell — is entirely nacreous. They also agree with the Nauti- 

 lus in the relative capacity of their last chamber, which seems 

 obviously large enough to contain the whole animal More- 

 over, it appears, from the position of the siphuncle and the 

 form of the aperture, that these shells were revolutely spiral, 

 or coiled over the back of the animal, and not involute like 

 the Spirvla. No traces of fossil ink (sepia) or horny claws 

 have been found associated with them, nor any indications of 



