INTRODUCTION. 49 



Mesomphix. " Umbilicus expanded, exhibiting the volu- 

 tions. 



Tkiodopsis. "Umbilicus large, lip thick, aperture nar- 

 rowed by three teeth, one upon each lip and one upon 

 the columella. 



XoLOTREMA. " Differs from the preceding by absence of 

 umbilicus ; or, it is small and covered by the reflected 

 lip ; aperture transversal, linear ; the inferior tooth a 

 lamellar carina. 



Chimotrema. " Aperture transverse, extremely curved, 

 resembling a simple fissure. 



ToxoTREMA. " Differs from the preceding by the emargi- 

 nate 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. 



Aplodon. " Aperture rounded, columella with a single 

 tooth; umbilicated. 



In his Enumeration and Account of Remarhable 

 Objects in his cwn cabinet, published at Philadelphia in 

 1831, Toxotrema and Stenotrema were changed to Tox- 

 ostoma and Stenostoma; two new genera, Trophodon 

 and Odomphium, and one sub-genus, jMenomphis, were 

 indicated by name, and the two following genera were 

 characterized : — 



Mesodon. " Differs from Helix by lower lip with a tooth. 

 Omphalina. " Differs from Helix by no lips, l)ut an 

 umbilicus. 



VOL. I. 6 



