PATULA. 155 



Fig. 62 shows the general arrangement of the teeth on the membrane. The 

 characters of the individual teeth are better shown on PL IV. 



Fig. 62. 



P. Cumberlandiana. 



There is a considerable difference in the lingual dentition of the species I 

 have grouped in this genus as to the development of the side cusps to the cen- 

 tral and lateral teeth, and the presence of distinct cutting points upon these 

 cusps. Such cusps and points are present in solitaria, alternata, perspectica, 

 slriatella, HempMlli, Idahocnsis, asteriscus. I do not detect these cusps in 

 P. strigosa, Cooperi, probably the same species, or Cumberlandiana, excepting 

 on the outer laterals. 



The central and lateral teeth of all the species examined by me are, in other 

 respects, as usual in the Helicea. It will be noticed that the base of attach- 

 ment is subquadrate, the reflected portion large (except in asteriscus), the cusps 

 short, the cutting points sho (-. 



All the outlines of the teeth are less graceful than in Zonites. The lateral 

 teeth are made asymmetrical by the suppression of the inner lower angle of 

 the base of attachment, and the less development, if not suppression, of the 

 inner cusp, which loses the cutting point also. The marginal teeth are quite 

 different from those of Zonites, Limax, Vitrina, Macrocyclis, and Glandina in 

 not being aculeate. They are more crowded than in those genera. They 

 have a quadrate base of attachment, not sole-like, shortened on its inner lower 

 side, but produced at its outer lower margin. The reflected portion is as wide 

 as the base of attachment, is more produced than in the central and lateral 

 teeth, retains its width throughout, and bears two oblique, blunt cutting points, 

 the inner one always much the larger and longer, and the outer one of which, 

 in most of the species, has a tendency to bifurcation. There is considerable 

 variation in these cutting points even in the same lingual membrane, but as a 

 general thing it may be said that the marginal teeth are but a modification of 

 the form of the laterals. They decrease in size greatly at the outer edge of the 

 lingual membrane. 



It must be borne in mind that the cutting points vary in development on 

 different portions of any one lingual membrane. I have in each case chosen 

 for drawing such individual teeth as appear best to illustrate the general char- 

 acter of the dentition. 



It will be seen that Patula differs from all the preceding genera by the 

 presence of quadrate, not aculeate, marginal teeth, a character shared by all 

 the succeeding genera. There does not appear any very essential character 



