500 LIMN^ID^. 



Planorhis armifjprua, Sat, Journ. Acad. Nat. Sc. ii. 164 (1818) ; Binxey's eel. 6.3. — Hal- 

 DEM.\N, Mon. 30, pi. 4, figs. 11-13 (1844). — Gould, Inv. 205, fig. 138 (1841).— 

 Adams, Shells of Vermont, 1.55 (1842). — De Kay, N. Y. Moll. 62, pi. 4, figs. 64 a, 

 b,c (1843). — Mrs. Gray, Fig. Moll. An. pi. 310, fig. 2. — Axon. Can. Nat. ii. 205, 

 fig. (1857). 



S&jmenlina armigera, H. and A. Adams, Gen. Rec. Moll. ii. 264, pi. 84, fig. 4. — W. G. 

 BiNNEY, Smith. Inst. L. and Fr. W. Shells, ii. 137, figs. 228, 229 (1865). 



Planorbella armir/era, Chenu, Man. de Conch, ii. 283, fig. 3570. 



Shell small, brownish horn color, or light chestnut, orbicular ; 

 right side nearly plane, with only a slight central pit, showing four 

 rounded volutions, distinctly separated by the suture ; left 

 *^'"' '^^' side deeply concave, exhibiting all the whorls, which on this 

 side arc sub-carinated ; surface shining, faintly marked by 

 the lines of growth, and, on the left side, may be distinctly 

 seen several raised revolving lines on each of the whorls ; ap- 

 erture slightly inclining to the left, rounded, and very slightly 

 modified by the carina, very oblique ; edge of lip dark brown ; at 

 some distance witbiii the throat are five white teeth, nearly closing 

 the passage ; a large, prominent, oblique one is situated on the side 

 of the preceding whorl, and may always be seen ; a very small one 

 is by its side ; opposite to them are the three others, which are 

 small. Larger diameter, five twentieths of an inch ; smaller diam- 

 eter, one tentli of an inch. 



Animal very active, of a l)lue-l)lack or slate color; foot long and 

 narrow. The shell is carried inclined at an angle of forty-five de- 

 grees. Tlie respiratory groove is very acutely pointed. 



Found abundantly in shady, stagnant pools and ditches, in which 

 an abundance of decaying vegetable matter is immersed. 



This common shell is well-marked by its external sim- 

 plicity. At the same time, the complicated armature of the 

 aperture, so unique in this family, would seem to entitle it 

 to be arranged as a sub-genus. It differs from the preced- 

 ■m>s''^a- ii-io- in havino; the umlnlicus on the left instead of the right 



Enlarged. o ^ o 



side, being its natural place. Mr. Plaldeman proposes to 

 make this species the type of a sul)-genus, which he calls Planorhula. 

 [Ranges from the Eastern through the Middle, Western, and 

 Northwestern States, and as far north as Peace River. 



Oeniis ANCYL,US, Geoffroy. 1767. 



Tentacles triangular, mantle included ; pulmonary orifice pro- 

 tected by a branchial appendage. Foot large. 



