﻿PEEFATOEY. 



The introductory portion of this Monograph contains descriptions of all the 

 sectional divisions of the genus with which the British Trigonia3 are connected. 

 The sketch of species in italics^ appended to these sectional divisions has been 

 reconstructed and amended in the Stratigraphical Table" at the end of the 

 Monograph, and to this the reader is referred. One division not referred to in 

 the introductory portion is the living section of the genus, the " Pectinidge " of 

 Agassiz, a section which is special to one of our colonial possessions, being known 

 only in Australia. This particular section will be found alluded to in the last 

 few concluding pages of the Monograph.^ 



The importance of the Trigonise both zoologically and stratigraphically 

 appears only lately to have been sufficiently estimated by either the naturalist 

 or the geologist. The gradually increasing occurrence of these forms, and 

 their relationship to the zoological assemblages with which they are connected, 

 may be considered as so many features of constantly increasing interest and 

 importance to science, whatever may be determined upon as to their status 

 whether as species or varieties. It is only within the last few years that 

 Tertiary Trigonige of the Pectinid^e group have been discovered in Australia. 

 The Tertiary formations of the other continents are, as far as we yet know, 

 entirely destitute of the genus. 



JOHN LYCETT. 



Scarborough ; 



lOtA February, 1879. 



1 Pages 5—13. - Pages 235—239. ^ Y&gts 231—234. 



