North American Helices. 35 



Descriptions of the principal Genera and Subgenera in which 

 certain North American Species of Helix are arranged hj 

 Alters, " Die Heliceen^ Zd Ed. 



GENUS XL 



Hyalina (Fer.) Gray. 



Testa plerumqnc umbilicata, tenuis, nitens, vitrea vel fusco-cornea ; 

 anfr. 5-7 regulariter accrescentes, ultimus non descendens, ssepe antice 

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

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



Animal : maxilla simplex (nee sulcata nee dentata), arcuata, margin e 

 inferiori acnto, medio rostriformiter prominente. Apertura respiratoria 

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

 simplex, sagitta amatoria ej usque bursa et follicnli mucosi omnino desunt ; 

 flagellum parvum vel nullum, musculus retractor penis brevissimus, 

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

 denticulati. 



1. Hyalina s. str. 



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

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

 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 

 reflexiuscnlo. Flagellum nullum ; bursa copulatrix apice angusta, canali 

 brevi. (Moq.-Tand.) 



4. Ammonoceras Pfr. 



Testa late et perspective umbilicata, depresse orbicularis, nitida, p«l'- 

 lucida, tenuis, radiatim striata; spira planiuscula ; anfr. 4-7 parnra e©n>- 

 vexiusculi, ultimus auctus, antice non descendens, ad peripheriam /otnn- 

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

 acutum, marginibus conniventibus. 



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

 Moll. I. 49. 



