53 



limits, considerable diversity of form and structure. Some of 

 them present traces of an umbilicus, especially those specimens 

 which are of the thinnest texture. The thin shells are some- 

 times more slender than the others. 



The opercles of the shells present also considerable diversity 

 of form ; in the largest (adults) the opercle is long and narrow, 

 closing the mouth of the aperture, in length, but not in width. 

 In the smaller shells, the opercle seems to close the shell com- 

 pletely, about one fourth of a turn back from the mouth of the 

 orifice. This shell corresponds well with DeKay's description 

 of P. Integra. (See Invert, of N. Y.) 



I have observed, that the structure of the animal in the re- 

 versed shell, is also reversed. 



About twelve miles south from Mohawk, in Schuyler's Lake, 

 are found great numbers of Paludina integra Say. The species, 

 as thus exhibited, is seldom over one inch in length, the shell 

 rather more slender than the specimens of P. decisa, which have 

 come under my notice in the canal and river, at Mohawk, and I have 

 never seen a single reversed specimen among them, notwithstanding 

 I have carefully examined hundreds of specimens in various stages 

 of growth, and at different times, to ascertain if they were pre- 

 sent. I have also examined Paludina, in other small lakes and 

 ponds having connection with the above-named lake, but have 

 never seen a single reversed specimen among them. 



From all I have been able to ascertain in relation to reversed 

 specimens of Paludina decisa, I am disposed to consider this 

 peculiarity as exclusively incident to this species ; and I regard its 

 occurrence as a distinct indication that the shell is P. decisa Say, 

 and also that the occurrence of occasional reversed specimens 

 among dextral shells of this genus, is a clear indication of the 

 species. 



Prof. William B. Rogers communicated some observations 

 recently made by him on the natural Coke, and the asso- 

 ciated igneous and altered rocks of the Oolite coal region 

 in the vicinity of Richmond, Virginia. 



In the district on the north side of the James River, where the 

 most valuable seam of coke has been explored, it is at present 



