3J:4 THE ETOLTJTIO?^ OF LIASSIC GASTEOPODS. [vol. Ixxvii. 



in constructing a classification of Gastropoda, and pointed out 

 how these have been used by Prof. Grabau in his studies of 

 Tertiary groups. The order of appearance of the spiral and axial 

 ornament will similarly prove useful in the study of the Liassic 

 gastropods which are referred to Troclius and Fleurofomaria. 



Dr. Truemais' thanked Dr. Bather and Dr. Davies for their kind 

 remarks. He agreed with the suggestions put forward b}^ the 

 latter speaker, that the axial ornament generall}^ coincides with the 

 groAvth-lines, and that the ribs arise by a rhythmic strengthening 

 of such lines. He pointed out that smooth shells are generally 

 thinner than the more ornamented species. The Authors had been 

 fortunate in securing a great number of small gastropods with 

 protoconchs complete, from the Liassic cla3^s ; but, unfortunateh', 

 specimens collected in limestones are not, as a rule, sufficiently 

 well preserved to show details of ontogeny. 



