PREFACE. 



This volume includes the letter press and plates containing the descriptions 

 and illustrations of the Lamellibranchiata, II, and constitutes a part of 

 Volume V, part I, of the Palaeontology of New York. 



I have already stated, in the preface to the preceding volume, that the 

 original intention was to publish the work as a volume of text and a volume 

 of plates; but the exigencies of publication made it necessary to issue the 

 work in two parfj^. The inconvenience attending this plan has arisen from the 

 necessity of adding other plates to the first part, in the Monomyaria, following 

 plate Ixxx; the plates from i to bcxx having previously been lithographed. 

 In the present volume, the few plates added to the Dimyaria have been num- 

 bered xciii to xcvi, following the last number in the preceding volume. 



These two volumes contain the descriptions and illustrations of all the well- 

 known and determined species of Lamellibranchiate shells from the Upper 

 Helderberg, Hamilton, Portage and Chemung groups, which formations are 

 recognized as belonging to the Devonian System ; together with a small number 

 of species from the Waverly sandstone, and rocks of corresponding age, which 

 are generally regarded as Lower Carboniferous. A few others have been 

 introduced for the sake of comparison, or to show the distinguishing features 

 of certain genera. The comparatively few species illustrated from the Waverly 

 group are not to be considered as affording full means of comparison with the 

 fauna of the groups below. 



In commencing this work, the author had conceived the plan of bringing 

 together illustrations of all the authentic and well-established genera of 

 Palaeozoic Lamellibranchiata; both in order to show the relations of those 



