136 THE CHICAGO ACADEMY OF SCIENCES. 



shells are thin and brittle, with a more or less flaring aperture, a gyrate 

 and imperforate axis and a simple peristome. 



The genus Lymncea has been credited to several authors (Bru- 

 guiere, Draparnaud, Montfort, etc.), but is clearly due to Lamarck, 

 who correctly diagnosed the genus in 1799. Bruguiere has frequently 

 been quoted as its author, although the reference in the Encyclopedic 

 Methodique is clearly referable to Lamarck, Bruguiere, as Dr. Ball 

 remarks, "having nothing to do with it." The name Lymncea has been 

 spelled in six different ways Lymnea, Lymncea, Lymnceus, Limnea, 

 Limntea and Limnaus. Etymologically the name should be spelled 

 Limnaa, but there seems to be no valid reason why Lamarck's original 

 spelling should not be used. If the law of priority is to be adhered 

 to strictly, there is then no other course. Some of the early American 

 conchologists spelled the name correctly, but during the last forty or 

 fifty years the name has been almost universally spelled Limnsea. Dr. 

 Pilsbry (Nautilus, XVIII, p. 63, 1906) was the first modern zoologist 

 to revise the original spelling, which has been generally accepted among 

 American conchologists. The name Limnaea was used by Poli in 1791 

 for a heterogeneous assemblage of pelecypods, but his curious quadri- 

 nomal system does not enter into systematic nomenclature. 



Lymnaea stagnalis (Linne). Plate XIX, figures 1-3. 



Helix stagnalis LINNE, Syst. Nat., Ed. X, p. 774, 1758; Ed. XII, p. 



1249, 1767. BAKER, Science, n. s., XXVII, p. 943, 1908. 

 Lymncea stagnalis LAMARCK, Prodr., p. 75, 1799. 



SHELL: Elongated (or oval), ventricose at the anterior end, thin; 

 periostracum yellowish-horn to brownish-black; surface shining, growth 

 lines numerous, crowded, more or less elevated, crossed by numerous 

 fine, impressed spiral lines ; apex smooth, brownish horn color ; whorls 

 six to seven, rapidly increasing, all but the last two rather flat sided; 

 last whorl very large, considerably dilated and inflated, inclining to 

 form a shoulder; spire long, pointed, acute, occupying about half the 

 length of the entire shell ; sutures distinct, sometimes impressed ; aper- 

 ture large, broadly ovate, dilated, particularly at the upper part; 

 peristome thin, acute, anterior part rounded ; parietal wall with a rather 

 wide, spreading callus which is closely appressed to the body and either 

 completely closes the umbilicus or leaves a very small chink; pillar 

 of the columella gyrate, usually forming a more or less heavy, oblique, 

 ascending plait. 



Aperture 



Length. Breadth, length. Breadth. 

 49.00 24.00 27.00 14.00 mill. Baden, Germany. 

 51.00 23.00 27.00 13.00 " 



