^34 THE NAUTILUS. 



BRIEF NOTES ON THE LAND AND FRESH-WATER SHELLS OF MERCER 



COUNTY, ILL. 



BY AVILLIAM A. MARSH. 



Sub-genus Planorhula, Haldcnian. 

 101. — Segmeutina armigera, Say. 



Shell varied in color, from very dark born color to almost white, 

 spire regular, slightly concave, suture well impressed, whorls four, 

 longer than wide, carinated above, aperture oblique, labrum 

 usually of a darker color on the edge. AVithin the aperture are five 

 teeth, two on the pillar lip, one near the anterior lip, one on the side 

 of the labrum, and two on tlie upper portion of the outer lip. This 

 interesting shell has a range from Maine to Colorado. It is rather 

 common here about our small ponds, being usually found associated 

 Avith P. exacutus and P. parvus. It may be found adhering to sticks, 

 bark and pieces of pine boards where the water is very shallow. 



ANCYLU8 Geoffrey, 1767. 



102. — Aneylus rividaris, Say. 



Shell pale yellow, opaque conic, depressed ; apex obtuse, nearer to 

 and leaning towards one side and one end ; aperture oval, rather 

 narrower at one end, entire. This shell is very abundant along the 

 margin of the Mississippi River ; found adhering to the limestone 

 rock in the river, also on limbs of trees, dead leaves and old valves 

 of Uniones. I have one valve of a Unio ellqms in my cabinet that 

 had 25 of the Ancylvs on it. 



103. — Aneylus parallelus, Haldeman. 



Shell pale, thin, fragile, lengthened, uai*row, apex rather short, 

 sharp, conspicuous, with two-fifths of the shell posterior to it. Inhabits 

 Pope Creek, in this county ; has neyer been found elsewhere. 

 When found at all it occurs veiy abundantly, adhering to sticks, 

 stones and dried leaves. I have found it attached to live specimens 

 of Pleurocera suhulare. 



104. — Aneylus tardus, Say. 



Shell conic, depressed, a\>ex behind the middle, obtuse, rounded, 

 inclining backward, line from the apex to the posterior tip rectilin- 

 ear ; line from the apex to the anterior tip arcuated ; aperture oval. 



