PREFACE. 



IZ 



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 diflference. 



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 Coimt 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 Atiiyris, 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 Leioriiynchds has been adopted for certain forms heretofore thus 

 referred. 



Under the pentameroid type it has been found necessary to propose, as 

 distinct genera, Pentamerella, Gypidcla, Anastrophia and Amphigenia, 



