152 mi-: PRESIDENTS ADDRESS. 



is divided into two orders. The naked cuttles, without an external 

 shell and breathing by two gills, form the Dibranchiata, like the 

 common outtle-fish. 



The i chambered shell, and breathing by four 



gills like tii" Pearly Nautilus, form the Tetrabranchiata. To the 

 Dibra I upposed, the animal of the Belemnite, 



whiob firBt appeared in the Lower Lias sea, but no ancestral form of 

 this mollusc is known in the Trias. It rapidly multiplied during the 

 Lie Lias time, and its internal bony skeleton is so abundant in some 

 strata that they were called the Belemnite beds by De la Beche, 



German geologists. All the naked 

 cuttles are furnished with an ink-bag, containing a dark-coloured 

 pigment, which is very miscible in water, and in some of the 

 specimens from the CTpper Lias this fossil pigment is well preserved. 



Tetrabrauchiates, with a many-chambered shell, are well 

 represented in all the Lias beds, the only living representative of 

 which is the Nautilus pumpilius. This family is theoldest; it com- 

 menced its career in the seas of Silurian times, and under many 

 singular generic forms it has lived on into the present day, and is 

 well represented by the Nautilus striatus from the Lower Lias of the 

 . new on the table, which closely resembles the Nautilus pom- 

 pilius of the Indian Ocean. 



The Ammonoida differ from the Nautiloida in having the side parti- 

 tions of ti nhers terminating in various angular or foliated 

 figures, seen in its highest complication in some Ammonite sh< LI 

 This order commenced in Devonian times with the genus GoniatUes, 

 the, flourished in the Devonian and Carboniferous seas and died out in 

 the Lias. They were succeeded in the Muschelkalk by the Geratites, 

 with small serrations on part of their lobe-line. The Hallstadt Trias 

 ■ 'ins a wonderful assemblage of Ammonit ■.-• possessing small compli- 

 cated lobe-lines of singular minute patterns, and these were succeeded in 

 the Lias by the Ammonites witli large highly foliated lob ■ lines. 



This group is divisible into four families. First, the Arcestidce ; 



second, tic Tropitida, which appertain almost entirely to the Trias, 



whilst the other two families -third, the Aegoceratida, and fourth, 



the Lytoceratid . are distributed in the Lias, Jurassic, and Cretaceous 



rocks; c, i ira in each family become leading fossils in differ int 



strata, so thai i the Lias sea was characterise,! 



by species of Ammonites found only in be, is of the same age and 



en, and which have a wide distribution in time and space therein. 



ras planorbis and Aeg. angulatum, are 



prol Triassic forms, of which, however, weal present 



knownothing. I iter,. up ! v , ith prominent keel and 



alcated Bipl t, are highly characteristic of the Lower Lias, 



itus, Conybeari, rotiformis, and semicostatu 



found only in theBe beds, as was long ago pointed out by Yon Buch. 



In the Middle leas the genus Aegoceras attains a great develop- 

 in. lit. and James ni, armatum, planicottatum, Henleyi, Davei, Valdani, 



