-M 



V I >. ntition of MoU\ 



UDcini (the fourth, fifth, and twelfth) to show variations 

 in l rin : also the thirteenth tooth in profile. 



. narrow, slightly arched, blunt at ends, with a 



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



Bpringing upwards from about the centre of tin: 



anterior sui ol the jaw, of the same color, material, and con- 



the jaw itself. This is not the muscular attachment 



■win 'i adheres to the jaw after it has been extracted. Jaw 



Lh delicate distant longitudinal 6trisB. 



Zoiiitc* laevigata, 



't'r. 



Land and Fresh-water Shells of North America, Part [., p. 

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



Pig. ■!. 



Lingual dentition of Zonitea laevigata, I'fr. 



by Dr. Leidy, prepared for, but oot published in, the "Terrea 

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

 zed on our recently obtaining the lingual membrane of 

 . 

 Teeth 17.1.17. arranged incurving transverse rows. Centrals 

 ■ i it. rounded at Bides, square at base, apex with three short 

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

 , pid, I ie outer cusp very short and sharp, the central cusp 

 bulging at sides, tapering to an acute point ; 

 • i -j. ale long as central cusp, narrow, pointed; third 



irth laterals merging into the uncini, which are acul< 

 . to the genera Zonites and Tlyalina. The centrals are 

 . plate, whose four aides curve rapidly inwards, 

 on plates long, narrow, curving outwards in 

 manii' i . 



