270 THE CHICAGO ACADEMY OF SCIENCES. 



UTAH : Deception Lake, 8 miles from Kanab, Kane Co. (Daniels and 

 Ferriss). 



GEOLOGICAL DISTRIBUTION : Pleistocene. 



RECORDS. 



MICHIGAN: Kegomic, Emmet Co., in marl beds (Slocum). 



ECOLOGY: On damp mud flats and in other situations similar to 

 those under which modicella is found. 



REMARKS: Rustica appears to be a modification of the humilis 

 type of shell, characterized principally by its long, very acute spire 

 and ovate aperture. Its long, pointed spire will distinguish it from 

 any form of modicella. It is liable to be confounded with forms of 

 Galba obrussa exigua, but in that race the aperture is longer and 

 narrower and inclined to be squarish, while in rustica it is more acutely 

 rounded at the extremities. The spire in rustica is longer and more 

 acute than in exigua, the spire whorls being less inflated. Half-grown 

 specimens of obrussa are similar in general form, but differ in the 

 form of the aperture, which is longer and narrower and forms a dis- 

 tinct shoulder at the junction of the outer lip with the body whorl, 

 while in rustica this part of the lip is gracefully curved. The aperture 

 is sometimes almost round and the spire varies much in height. Rustica 

 is evidently more nearly related to modicella than to obrussa and may 

 be considered a variety of humilis. 



The type of rustica is not in the Smithsonian collection and is 

 probably lost. Lea's description and the figure in Binney's work, how- 

 ever, leave no doubt as to the kind of shell Lea had in mind. A single 

 specimen in the Lea collection in the Smithsonian Institution is marked 

 rustica and agrees fairly well with Lea's description. It is No. 118652, 

 Careful search will undoubtedly reveal this neat little variety in many 

 collections, labeled humilis or obrussa. 



Galba obrussa (Say). Plate XXVT, figures 8-13; plate XXXI, 

 figures 20-37. 



Lymneus obrussus SAY, Journ. Phil. Acad., V, p. 123, 1825 ; Binney's Ed., 

 p. 113, 1858. 



Lymncea obrussa GOULD, Lamarck's Genera, p. 69, 1833. WHEATLEY, Cat. 

 Sh. U. S., p. 23, 1843. JAY, Cat., p. 270, 1852. DALL, Land & F. W. Sh., p. 73, 

 fig. 51, 1905. BAKER, Bull. 111. State Lab., VII, p. 103, 1906. HENDERSON, 

 Univ. Col. Studies, IV, pp. 93, 179, fig. 34, 1907 ; Univ. Col. Studies, IV, p. 158, 

 1907. DANIELS, Nautilus, XXII, p. 120, 1909. WALKER, An. Rep. Mich. Geol. 

 Surv., 1908, p. 290, 1909. BAKER, Nautilus, XXIII, p. 94. BERRY, Nautilus, 

 XXIV, p. 62, 1910. 



Limnaus obrussa KUSTER, Conch. Cab., p. 51, taf. 11, fig. 19-21, 1862. 



Limnaa obrussa BINNEY, Check List, p. 12, 1860; Land & F. W. Sh. N. A., 

 II, p. 49, fig. 69, 1865. TRYON, Amer. Journ. Conch., Ill, p. 196, 1867. WOOD, 

 Nautilus, V, p. 54, 1891. KEEP, West. Amer. Sh., p. 314, 1904. 



