448 

 chamber 



Mr. R. Kirkpatrick on tlie Structure of 



each system grouped round its central and circum- 

 ambient chamber. Young specimens of Lahechia conferta 

 sliowed in the earliest stage a thin disk formed of forty or 

 fifty spiral coils. Later the gradually ascending spiral led to 

 the formation of a solid cone standing on its apex, and still 

 later to the great hemispherical masses commonly met with. 



Fii?. 1. 



Ofbitulites complanata, Lamarck, showing central and circuniauibieut 

 chamber and succeeding spirals divided into segments. X 35. 

 (From Carpenter, ' Challenger ' Report on Orhitolites, pi. vi. tig. 2.) 



Fig. ± 



Lahechia conferta. Silurian, Gothland. Young specimens : side A-ieW 

 and view of under surface ; spiral growth indicated. Natural size, 



The extension in the horizontal plane partly takes place by 

 the formation of a central chamber in the course of some 

 particular coil, but mainly by the widening out of the spiral 



i 



