North American Helices. 21 



Maxilla costis numerosis, parum prominentibus, margine cretiato. Fol- 

 liculi mucosi, sagitta, capreolus, flagellura desunt. 



15. PoLTGYRA Say. 



T. umbilicata vel perforata, orbiculato-planata, oblique costnlato-stri- 

 ata; anfr. S-Y^^ lente accresceiites, ultimas antice constrictus, breviter 

 deflexus, basi inflatus, devians, penultimus plane conspicuus, perfora- 

 tiouem ssepissime riraatim constringens; apertura subreniformis vel irre- 

 gulariter sinuata; perist. anguste reflexum, callosnm, marginibus inter- 

 duQi dentatis, callo triangular!, deiitiforrai, in parietem aperturialem 

 oblique intrante junctis. 



16. Stenotrema* Raf. 



T. obtecte perforata, lenticularis vel globoso-depressa, pilosula ; anfr. 

 4J-6, ultimus antice gibbus, breviter deflexus, basi turaidus ; spira 

 parum elevata ; perist. albo-labiatura, margine supero breviter reflexo, 

 basnli strictiusculo, saepe sinuoso dentato. 



In quarta parte circuitus anfractus ultimi ante aperturam, columella 

 appendice callosa, lamelliformi, cavationem anfractus coarclante, munita 

 est. 



17. TRioDOPSisf Raf, 



T. obtecte perforata vel umbilicata, orbiculato-depressa vel subglobosa, 

 plus minus oblique striata; anfr. 5-7, ultimus antice paululum de- 

 flexus; apertura sinuoso-coarctata, subtriangularis ; perist. albo-callo- 

 sum, late angulatim reflexum ; paries aperturialis dente valido, oblique 

 intrante munitus. Maxilla costis 8-5, prominentibus, margine dentato. 

 Folliculi mucosi 2, simplices. (Moq.-Tand.) Sagitta 1 subconica, parum 

 arcuata, basi biangulata, elongata. (Ad. Schmidt.) 



18. MesodonJ Raf. 



T. umbilicata vel obtecte perforata, subglobosa vel orbiculato-depressa, 

 tenuis, subtiliter striata, interdum decussatim sculpta; anfr. 5-6 regulares ; 

 apertura rotundato-lunaris, interdum dente parvulo in pariete aperturiali 



* " Chimotrema. — Aperture transverse, extremely curved, resembling a simple 

 fissure. 



"ToxoTREMA. — Differs from the preceding by the emarginate lip. 



*' Stenotrema. — Differing from the two preceding by a thick emarginate lip, and 

 a second lip flattened to the spire and uniting with the true lip; a transversal 

 carina above." — Eaf. Vide.2l3rr. Moll. I.e. 49. 



f "Triodopsis. — Umbilicus large, lip thick, aperture narrowed by three teeth^ 

 one upon each lip and one upon the columella." Raf. Yide Terr. Moll. I. c. 49. 



X " Mesodon. — Differs from Helix by lower lip with a tooth." Raf. Vide Terr. 

 Moll. I c. 49. 



