484 



MICHIGAN SURVEY, 1905. 



ZONITOIDES ARBOREA (Say). 



Shell umbilicated, depressed, very slightly convex, thin, pellucid; 



amber-colored, smooth with microscopic revolving lines, shining; 



whorls 4-5, with very minute oblique microscopic strise ; suture well 



mpressed; aperture transversely rounded; peristome thin, acute; 



umbilicus moderate, well developed, round and deep. 



Alt. 2f , greater diam. 5, lesser 4^ mm. 



■■:/ -J 



Helix arhorea, Say, Nich. Encycl. pi. IV., fig. 4, (1817). 



Zonites arhoreus, W. G. Binney, Man. Am. Land Shells, 61, fig. 13, (1885). 



Helix , Sager, Doc. H. Rep. Mich., 1839, 420, separate, 14. 



arborea, Miles, Rep. Geol. Surv. Mich., 235, (1861). 



Hyalina , Currier, Shell-bearing Moll. Mich., 4, (1868). 



, DeCamp, Shell-bearing Moll. Mich., 5, (1881). 



Zonites arhoreus, Walker, Rev. Moll. Fauna Mich., 16, (1894). 



This is the most common species of the family, and is found abundantly 

 everywhere. Usually associated with Vitrea hammonis, V. indentata, V. 

 wheatleyi, and Zonitoides nitida. For the differential characters, see the 

 keys and the remarks under the several species cited. 



Subgenus PSEUDOHYALINA Morse. 

 Surface closely striate, ribbed or costulate. 



KEY TO THE SPECIES OF PSEUDOHYALINA. 



I. Surface striate. 



a. Shell larger, 5.5 mm. in diameter limatula. 



aa. Shell minute. 2.5 mm. in diameter minuscula. 



II. Minute, diameter 2\ mm. or less, surface ribbed or costulate. 



a. Surface ribbed, ribs oblique to lines of growth exigua. 



aa. Surface costulately [folded and reticulated with longitudinal ribs, 

 very minute milium. 



ZONITOIDES LIHATULA Ward. 



Fig 59. Z. limitul".. X4i. 



Shell small, widely umbilicated, depressed, thin, greenish- white ; whorls 

 rather more than 4, convex, with fine, oblique, parallel striae, becoming 

 subobsolete in the base; suture well impressed; aperture subcircular; lip 

 thin, acute, its ends approaching; umbihcus round and deep, exhibiting all 

 the volutions. 



