PREFACE. 
ix 
rocks in the West, than it does with that of the strata of the same absolute 
age in Eastern New York and in the adjacent portions of Pennsylvania. 
Having already, many years since, presented these views, it is not neces¬ 
sary to go farther into the discussion in this place, but merely to remark 
that further observations and the examination of more extensive collections 
have confirmed the opinion then expressed, namely, that the distinction 
between the Devonian and Carboniferous systems is one of geographical 
rather than geological difference. 
In the study of the . Brachiopoda, a few changes have been found neces¬ 
sary, beyond what has already been published in the Annual Reports upon 
the State Cabinet; and some additions have been made to our knowledge 
of the characters of established genera. In the Genus Chonetes, the 
observations first made by Count Keyserling (but subsequently doubted) of 
the oblique direction of the tubular spines as they penetrate the substance 
of the shell along the cardinal line, have been confirmed. 
In the shells of productoid form, which are sometimes referred to 
Productus and sometimes to Strophalosia, it has been shown that the narrow 
area and other external features of the latter genus are accompanied by 
the vascular imprints of the former. The numerous forms of this character 
give, to the fauna of the Chemung group, an expression quite similar to 
that of some of the Carboniferous rocks of the Mississippi valley. 
Some additional knowledge has been obtained, regarding the structure 
of the internal spires in the Genera Athyris, Meristella, and allied forms. 
It has appeared desirable to separate, under the sub-generic term 
Stenocisma, many of the species hitherto referred to Rhynchonella ; and 
the Genus Leiorhynchus has been adopted for certain forms heretofore thus 
referred. 
Under the pentameroid type it has been found necessary to propose, as 
distinct genera, Pentamerella, Gypidula, Anastrophia and Amphigenia, 
2 * 
