ZONITIDAE 65 



made by previous conchologists. It may be more convenient for 

 some people to use the old names but, since such use would be 

 incorrect at the present time, it is much better to become familiar 

 with the new names and to use them. 



Key to Genera 



1. Shell 3^ inch or more in diameter 2 



Shell 3^ inch or less in diameter 3 



2. Body whorl increasing greatly in diameter, p, 66; aperture 



round, without callus on base Mesomphix, p. 65 



Body whorl not greatly increasing in diameter; aperture 

 lunate, with yellowish callus at base Ventridens, p. 81 



3. Shell about ^^ inch in diameter 4 



Shell less than ]/% inch in diameter 6 



4. Body whorl greatly enlarged toward aperture. . .Retinella, p. 69 

 Body whorl not enlarged toward aperture; whorls evenly 



coiled, p. 79 5 



5. Shell with 4 whorls; base rounded Zonitoides, p. 78 



Shell with 6 whorls; base flattened Paravitrea, p. 73 



6. Spire elevated, dome shaped; diameter equal to or less than 



height; whorls 6; aperture not extending beyond contour 



of whorls Euconulus, p. 75 



Spire flattened; diameter greater than height; whorls 4; 

 aperture extending well beyond contour of whorls, p. 72. . . .7 



7. All whorls increasing regularly in size, last or body whorl not 



expanding toward aperture; umbilicus deep and round . . 



Hawaiiay p. 72 



\\\ whorls increasing rapidly in diameter, last whorl notably 

 expanding toward aperture; umbilicus shallow and oval, 

 whorls loosely coiled around it Striatura, p, 77 



Genus MESOMPHIX Rafinesque 



This genus includes the species of the family Zonitidae 

 having the largest shells. In this genus, the aperture as well as 

 the shell itself is relatively large. 



Key to Species 



1. Base of shell smooth and shining, greenish or yellowish 



colored; upper surface ribbed and brown 



perlaevis vulgatus, p. 68 



Surface of shell uniform in texture and color above and below. .2 



2. Aperture round; interior of aperture violet or purplish 



friabilis, p. 67 



Aperture obliquely ovate; interior of aperture pearly 



cupreus, p. 66 



