INTRODUCTION. 49 
Mesomphix. " Umbilicus expanded, exhibiting the volu- 
tions. 
Triodopsis. " 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 Unumeration and Account of Remarkable 
Objects in his own 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, Menomphis, were 
indicated by name, and the two following genera were 
characterized : — 
Mesodon. " Differs from Helix by lower lip with a tooth. 
Ojiphalina. " Differs from Helix by no lips, but an 
umbilicus. 
vol. 1. 14 
