24 



THE NAUTILUS. 



Lateral teeth two in each valve. 



Muscular impression deep, poste- 

 rior one rough. 

 Nacre pearly-white. 

 Length 2.2. in. 

 Alt. 2.1 in. 

 Diam. 1.5 in. 



Lateral teeth thick and curved in 

 a direction over the cardinal 

 tooth. 



Anterior and posterior cicatrices 

 both distinct. 



Nacre pearly-white and iridescent. 



Length 2.3 in. 



Alt. 2.0 in. 



Diam. 1.5 in. 



If then, our contention is correct as to the absolute specific iden- 

 tity of the two species, priority must be given to Barnes's name and 

 the synonomy must be written as follows: 



QUADRULA UNDATA (Barnes). 



1823, Unio undatus Barnes, Am. Jl. Sci. VI, p. 121, pi. IV, fig. 4. 

 1831, Unto trigonus Lea, Tr. Am. Phil. Soc. IV, p. 110, pi. XVI, 

 fig. 40. 



EXPLANATION OF PLATES I AND II. 



PI. 1 fig. 1. Q. undata, Facsimile of one of Barnes's figures. 



PI. 1 fig. 2. Copy of Barnes's other figure. 



PI. 1 fig. 3. Q. undata, Fox River, 111. (original). 



PL II fig. 1. Facsimile of Lea's figure of Unio trigonus. 



PI. II fig. 2. Q. trigona Lea, Ohio River (original). 



PI. II fig. 3. Q. obliqua Lam. Paint Rock River, Jackson Co., 

 Ala. (original). 



NOTES. 



THREE SHELLS NOT HITHERTO REPORTED FROM THE DISTRICT 

 OF COLUMBIA. Recent collecting has added the following hitherto 

 unreported shells to the fauna of the District of Columbia or its en- 

 virons : Polygyra palliata Say (on the Virginia side of the Potomac 

 near Great Falls) ; Zonitoides milium Morse, Punctum pygm&um 

 Drap G. DALLAS HANNA. 



The albino Oliva angulata, noticed in the March number, has now 

 found a home with the Academy of Science at Minneapolis, Minn. 

 A. L. HETTRICH. 



