214 AMERICAN JOURNAL 



long, subquadrate, with incurving sides and base ; apex broad, 



recurved, tricuspid, the median cusp prolonged into a beak-like 

 Fig. 6. point. First lateral long, 



narrow, irregular, oblique, 

 with a recurved, tricuspid 

 apex as in the central. 

 Second lateral somewhat 

 the shape of the first lat- 

 eral, but shorter, less ob- 

 lique and less irregular, 

 its recurved apex produced 

 into longer and more del- 

 icate beaks. Third lat- 

 eral shorter, stouter, ir- 

 regular, jaw-shaped, bear- 

 M. bitubeiTulatum. ing on its inner or lower 



edge one median stout, and two terminal more slender beaks. 

 Figure 6 is drawn from a photograph taken directly from the 



lingual membrane by our friend Mr. Sam. Powel, of Newport, 



to whom we are indebted foi- nuich assistance in stud^nng lingual 



membranes. 



In our figure the teeth are separated from each other to clearly 



show their characters. On the membrane they are much more 



closely united. 



Helicina orbiculata, Say. (Plate 9, fig. 5.) 



An opportunity of examining the lingual membrane of this 

 species has lately been given us b}"" Dr. E. R. Schowalter, of 

 Uniontown, Alabama. We have examined numerous individuals 

 received from him, and find several points of interest in them. 

 The figure copied from Troschel in Land and Freshwater Shells 

 of N. A., Part III., p. 108, does not give clearly the outline of 

 the fifth lateral tooth. 



We give a figure of this lateral as it appeared to us, (Plate 

 9, fig. 5.) There is considerable variation in the shape of these 

 teeth, the basal expansion being often longer than in the one 

 figured. 



The uncini have long fringe-like points to the cusps of their 

 recurved apices. The outer uncini have more than three cusps ; 

 we have counted distinctly four and six on some. 



The uncini are very numerous, more than fifty on each side of 

 the membrane. 



