Dentition of Pulmonata. 39 



Jong, stout, lance-like cutting point, extending below the base of attach- 

 ment to a sharp point, and bearing at the centre of its length on each side 

 a prominent, subobsolete, blunt spur. There are three lateral teeth of 

 the same type as the centrals, but made unsymmetrical by the suppres- 

 sion of the inner lower lateral expansion to the base of attachment, and 

 the inijer subobsolete lateral spur to the cutting point. The fourth tooth 

 from the central tooth changes suddenly into a marginal tooth of the form 

 common in Orthalicns, i.e., along, stout, subquadrate base of attachment 

 with fringed lower margin, bearing at its lower portion, a broad, bluntly 

 rounded subobsolete cusp, from which springs a short, widely expanded, 

 broad, bluntly rounded, gouge shaped cutting point, which has a small, 

 outer, lateral spur of the same bluntly rounded form. This form of mar- 

 ginal teeth runs quite to the edge of the membrane, those nearer the 

 outer edge being smaller, more widely separated, and in more oblique and 

 more widely separated rows. 



Pig. A gives a central tooth with adjacent teeth to the fifth tooth on 

 one side, and only one lateral on the other side: fig. C gives the eighth 

 tooth ; fig. D two extreme marginals ; fig. B an extreme marginal in 

 profile. 



The count of the teeth in one transverse row is over 108-1-108. 



Peculiar as this form of dentition seems, it has already been noticed in 

 Liguus virgineus. (See Am. Journ. Conch., VI, 209, fig. 3, 4, and below 

 pi. III). That species differs widely, however, in the lesser size of its 

 membrane (10 X 4£ mill.), the smaller count of the teeth, 40-1-40, and 

 in having but two well marked laterals. That species also has several 

 teeth intermediate between the laterals and marginals which vary greatly 

 on different parts of the membrane. 



This form of dentition is very instructive in showing the 

 modification of the type usual to the Helicince. The central 

 teeth may be said to be obsoletely tricuspid, and the side 

 spurs to the greatly produced cutting point are but a modifi- 

 cation of the usual cutting points on the side cusps of the 

 Helicince. The lateral teeth are in the same way but a modi- 

 fication of the usual bicuspid laterals of the Helicince. The 

 marginal teeth are more abnormal in form, but they still are 

 but modified from the laterals by the expansion, bluntly 

 rounding and shortening of the cusps, and by the still greater 

 expansion, shortening and bluntly rounding of the cutting 

 points. In Orthalicus iostomus, melanochilus, undalus and 

 Liguus fasciaius, this process of suppressing the usually 

 decided cusps and cutting points is extended equally to the 

 central and lateral teeth. Other species show the same aber- 



