64 [Assembly 



certain and partially defined genus of Eafinesque. With such au- 

 thority before me, I adopted the generic name Leptana, and it has 

 not been until a later period that the researches of Mr. Davidson 

 have fully established, in Europe, the genus Strophomena. 



The difficulties attending the proper distribution of the Brachio- 

 poda were scarcely less at the time of the publication of the second 

 volume; and I there intentionally avoided proposing new genera, 

 waiting for the appearance of Mr. Davidson's work " On the Clas- 

 sification of the Brachiopoda." This important treatise, which, in its 

 several editions in different languages, has thrown so much light 

 upon the intimate structure, organization, and habits of this class of 

 fossils, has given a new impulse to their study, and has rendered 

 them of far greater geological value than ever heretofore. 



Notwithstanding however the great extension of genera proposed 

 by Mr. Davidson and by other English and Continental naturalists, 

 the field appeared to me far from being fully explored; and after 

 proposing several genera in addition to those already described, I 

 have still material for others, though not yet satisfactorily deter- 

 mined. 



In correcting the list of Brachiopoda, I have referred the species 

 as far as possible to established genera, and have endeavored to 

 indicate all cases of doubt by the simple ? or by some remark. 



I had hoped to be able to devote more time to the preparation of 

 this Catalogue; but to give it in all respects as I could wish, re- 

 quires a re-examination of a large number of the species, and such 

 a revision of the arrangement as would present the whole in a more 

 connected form. This work I propose to complete as early as pos- 

 sible; offering in the mean time the following imperfectly corrected 

 catalogue, which may be of use to the students in American Pa- 

 Iseontology. 



