no 



STUDIES IN LIFE AND SENSE. 



the oldest members of the -cuttlefish race. The Nautilus genus itself 

 begins in the Upper Silurian rocks : we may trace the well-known 

 shells upwards to the Carboniferous strata, where they are best de- 

 veloped ; and we follow the genus onwards in time, as it decreases 

 in numbers, until we arrive at the existing order of things, in which 

 the solitary nautilus remains, as we have seen, to represent in itself 



the fulness of cepha- 

 lopod life in the oceans 

 of the past. The older 

 or Palaeozoic rocks 

 reveal a literal wealth 

 of these chambered 

 shells, and therefore 



FIG. 10. SHELLS OF FOSSIL CUTTLEFISHES. 

 i, Turrilites ; 2, Baculites ; 3, Hamites ; 4, Scaphites. 



FIG. ii. SPIRULA. 



of the existence of the four-gilled cuttlefishes as the founders of the race. 

 When we ascend to the Mesozoic rocks (ranging from the Trias to 

 the Chalk), we meet with new types of the chambered shells well-nigh 

 unknown in the Palasozoic period. In the Mesozoic rocks appears 

 the fulness of Ammonite life. Here we find shells named after the 

 horns of the Egyptian god, Jupiter Ammon ; these, instead of being 

 tolerably plain like the Nautilidtz^ exhibit beautifully sculptured out- 

 lines, and folded septa, or partitions, between the chambers of the 

 shell. The shells allied to Nautilus and occurring in the Palaeozoic 

 formations differ from Nautilus chiefly in their varying degrees of 

 curvature or straightness. Lititites is a curved form allied to Nautilus ; 

 whilst Orthoceras&&& Gomphoceras are groups representing the straight- 

 ened forms. But in the Silurian period more complex forms appear, 

 with elaborate and folded septa. These are the early Ammonites, 

 such as Goniatites and Bactrites. In the Secondary rocks we find 

 the still more complex true Ammonites themselves. Here the lobes 

 and saddles of the shells, as the edges of the septa are named, are 

 of the most elaborate patterns, whilst the shapes of shell are of 

 the most varied character (Baculites, Turrilites^ Ammonites, &c., 

 fig. 10). 



There is an advance and progression exhibited in the de- 



