Nortli American Helices, 19 



Descriptions of the principal Genera and Subgenera in which 

 certain North American Species of Helix are arranged hy 

 Alhersj " Hie Heliceen,^^ 2d Ed. 



GENUS XI. 



Hyalina (Fer.) Gray. 



Testa plerumquc urabilicata, tenuis, nitens, vitrea vel fusco-cornea ; 

 anfr. 5-7 regiilariter accrescentes, iiltimns non descendens, sjepe antice 

 dilatatus ; spira depressa, rarissime orbiculato-conica ; apertura rotun- 

 dato-lunaris ; perist. tenue, acutum, rectum. 



Animal : maxilla simplex (nee sulcata nee dentata), arcuata, margine 

 inferiori acato, medio rostriformiter prominente. Apertura respiratoria 

 latere dextro supra collare, genitalis ad basin colli. Systema sexuale 

 simplex, sagitta amatoria ejusque bursa et folliculi mucosi omnino desunt ; 

 flagellum parvum vel nullum, musculus retractor penis brevissiraus. 

 Dentes linguae (radulse) laterales elongati, hamiformes, lateribus non 

 denticulati. 



1. Hyalina s. str. 



Testa umbilicata interdum perforata, depressa, vitrea, nitida; anfr. 

 5-6 regulariter accrescentes; spira rarissime conico-elevata ; aportura 

 rotundato-lunaris; perist. tenue, acutum, rectum. 



Flagellum breve (Moq.-Tand.). 



2. Mesomphix* Raf. 



Testa umbilicata vel perforata, globoso-depressa, tenuis, striatula, 

 fusco-cornea, subtus pallidior, nitida ; anfr. 4^-6, apertura lunari-ovata ; 

 perist. simplex, rectum, acutum, marginibus conniventibus, columellari 

 reflexiusculo. Flagellum nullum ; bursa copulatrix apice angusta, canali 

 brevi. (Moq.-Tand.) 



4, Ammonoceras Pfr. 



Testa late et perspective umbilicata, depresse orbicularis, nitida, pel- 

 lucida, tenuis, radiatim striata ; spira planiuscula ; anfr. 4-7 parum con- 

 vexiusculi, ultimus auctus, antice non descendens, ad peripheriam rotun- 

 datus ; apertura perobliqua, ampla, rotundato-lunaris ; perist. simplex, 

 acutum, marginibus conniventibus. 



* " Mesomphix umbilicus expanded, exhibiting the volutions." Raf, Vide Terr. 

 Moll. I. 49. 



