284 Notes on Lingual Dentition of Mollusca. 



several uncini (the fourth, fifth, and twelfth) to show variations 

 in their form ; also the thirteenth tooth in profile. 



The jaw is long, narrow, slightly arched, blunt at ends, with a 

 slight, broad, median projection. There is a long, narrow, coni- 

 cal projection springing upwards from about the centre of the 

 anterior surftice of the jaw, of the same color, material, and con- 

 sistency as the jaw itself. This is not the muscular attachment 

 which often adheres to the jaw after it has been extracted. Jaw 

 with delicate distant longitudinal striae. 



Zoiiites laevig-ata, Pfr. 



(See Land and Fresh-water Shells of Korth America, Part L, p. 

 287.) The wood-cut here given was engraved from a drawing 



Fig. 4. 



mmtrnM 



Lingual dentition of Zonites laevigata, Pfr. 



by Dr. Leidy, prepared for, but not published in, the " Terres- 

 trial Mollusks of the United States." The drawing was at once 

 recognized on our recently obtaining the lingual membrane of 

 the species. 



Teeth 17.1.17, arranged in curving transverse rows. Centrals 

 short, stout, rounded at sides, square at base, apex with three short 

 and pointed cusps, the middle one longest. Laterals long, narrow, 

 tricuspid, the outer cusp very short and sharp, the central cusp 

 extremely long, bulging at sides, tapering to an acute point ; 

 inner cusp almost as long as central cusp, narrow, pointed ; third 

 and. fourth laterals merging into the uncini, which are aculeate, 

 as common to the genera Zonites and Hyalina. The centrals are 

 on a long, narrow^ plate, whose four sides curve rapidly inwards. 

 The laterals are on plates long, narrow, curving outwards in 

 an arcuate manner. 



