180 THE CHICAGO ACADEMY OF SCIENCES. 



Washington and Chicago. It is the largest species of the genus 

 found in the United States, and may be known by its flat form, 

 very transverse aperture, deep umbilicus and indented umbili- 

 cal region. It has been found somewhat plentifully in the 

 greenhouses at Lincoln Park, Chicago, but is particularly large 

 and fine in the greenhouses at Washington Park, where it is 

 found beneath old boards under the flower pot shelves. Speci- 

 mens have been found here measuring over half an inch in di- 

 ameter. It has not been found outside of the greenhouses.* 



FIG. 36. 



Comparative figures of VITREA and ZONITOIDES. (After Morse, 

 Amer. Nat., Vol. 1, Nos. 8 and 10.) Enlarged. 1, ZONITOIDES ARBOREUS 

 Say; 2, VITREA HAMMONIS Strom; 3, VITREA INDENTATA Say; 4, ZON- 

 ITOIDES MINUSCULUS Binney. 



67. Vitrea Hammonis Strom, pi. xxviii, fig. 10. 



Helix hammonis STROM, Act. Nedross., Vol. Ill, p. 435, pi. vi., fig. 16, 



1795. 



Helix radiatula ALDER, Cat. North and Durh., p. 12, No. 50, 1848. 

 Helix virtdula MENKE, Syn. Meth., ed. 2, p. 127. 

 Helix striatiila GRAY, non Linne, nee Muller; undescribed. 

 Helix nitidosa FERUSSAC; undescribed. 

 Helix electrina GOULD, Inv. Mass., p. 183, fig. Ill, 1841. 

 Helix pura PFEIFFER, Binney, non Alder. 

 Helix virtdula PFEIFFER, <?.r/arte, 1848,'non 1881; Binney apud Pfeif- 



fer, non Menke. 



Helix hammonis WESTERLUND, Morch, Pfeiffer, 1881.| 

 Hyalina pellucida LEHNERT, Science Record, June, 1884, p. 141. 



Shell: Small, depressed, thin, umbilicated ; surface shining, 

 the lines of growth well marked, impressed, more or less equi- 



*Mr. W. W. Calkins has reported the finding of Zonites alliarius Muller in Chicago 

 greenhouses, but thus far the record has not been substantiated. All of the specimens 

 have been draparnaldi. 



tFrom Ball, Proc. U. S. Nat. Mus., 1885, p. 269. 



