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posed a local bed of Carboniferous rocks, until we saw the 

 same associated with the other forms in Major Hawn's col- 

 lections), apparently two distinct species, undistinguishable 

 in form, and surface markings, as well as muscular and pallial 

 impressions, from the genus Pleurophorus, established by Mr. 

 King for the reception of a Permian shell. Along with 

 these, in Major Hawn's collections, there are also several 

 specimens of a small shell, having, as far as can be deter- 

 mined from its form and general aspect, the characters of 

 the Permian genus Bakevellia. Indeed it appears to be al- 

 most specifically identical with B. antiqua, of Munster, a 

 characteristic species of the Permian rocks of England and 

 Germany ; though on comparison with specimens of this 

 species, now in the New York State Geological Collection, 

 sent over recently from England, by Sir Roderick Murchi- 

 son, we think we can see specific differences. 



There are likewise from this rock, both in Major Hawn's 

 and Dr. Cooper's collections, specimens of a well marked 

 Monotis, a genus regarded, so far as we know, by all Palae- 

 ontologists, as having been introduced during the Permian 

 epoch. We are aware many authors regard the genus 

 Monotis of Bronn as only a section of the genus Avicula ; 

 but whether we view it in this light or not, does not affect 

 the question in regard to its being a peculiar type dating 

 back, according to generally received opinions, no further 

 than the disposition of the Permian rocks. In addition to 

 this, the species under consideration (M. Hawni of this 

 paper) presents so many points of similarity to some varie- 

 ties of the Permian species, M. Speluncaria, of Schlotheim, 

 as figured by Mr. King in his work on the Permian Fossils 

 of England, that it is not always easy to point out characters 

 by which they can be distinguished. 



It is true the condition of these fossils is such, being 

 mostly casts, that their generic characters can not always 

 be made out beyond a doubt ; but from the unquestionable 

 relations of some, and the apparent affinities of others, taken 



