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 Paleontology 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 parts. The inconvenience attending this plan has arisen from the 
necessity of adding other plates to the first part, in the Monomyaria, following 
plate lxxx; the plates from i to lxxx 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 
