142 [January, 1842. 



cifically the same. He adds, that Mr. Audubon has now com- 

 pared these two ducks, and is satisfied that they are distinct 

 species. 



Mr. T. A. Conrad read a paper intended for publication in 

 the Journal, entitled, " Observations on the Silurian and 

 Devonian systems of the United States, with descriptions of 

 New Organic Remains." This memoir embraces descrip- 

 tions of 103 new species, included in 21 genera, viz. 



Avicula 23 species. Cypricardita, 6. Inoceramus, 3. 

 Microdon, 1. Moculites, 2. Plurorynchus, 3. Strophomena, 

 21. Delthyris, 13. Or'this, 1. Atrypa, 6. Helicoceras, 1. 

 Orthoceras, 1. Goniotites, 1. Belerophon, 3. Pleuratoma- 

 ria, 7. Euornphalus, 1. Loxonema, 1. Cyrtoceras, 1. Asa- 

 phus, 2. Calymene, 1. 



The paper was referred to a committee with a view to 

 immediate publication in the 2d part of the 8th volume of 

 the Academy's Journal, now in press. 



Professor Rogers announced that his brother Professor William 

 B. Rogers, of Virginia, has recently satisfied himself of the geologi- 

 cal age of the coal formation of the vicinity of Richmond ; and also 

 of the date of the Fredericksburgh sandstone. The former he re- 

 gards as nearly equivalent in period to the lias of Europe, and the 

 laiter to be referable to that of the oolite. The existence in the 

 Richmond coal measures of the genus Tseniopterus, a race of 

 plants strictly characteristic of the lias, is one of the points upon 

 which he rests his conclusions respecting that formation. A dis- 

 covery in the Fredericksburg sandstone of fossil cycadeae and 

 other organic remains, lead hirn to place this rock in the period 

 of the oolites. He considers those the only formations yet recog- 

 nised in the United States, which are referable to the ages of the 

 European Lias and Oolite rocks. 



