ZONITKS. 



95 



lasmndou, mnUidcntata., viridiibis, imlentatus^ fulvns, nitidus, Umatulua) arc so 

 fharactt'riziMl, and 1 lu'lU'vi; all will prove to be so. 



The nature of the \)0\\\ is described under Z. ftiliginosus. 



The external orifice of the generative organs in the species I have examined 

 is ([uite under the mantle, not on tlie rit^lit side of tlie head, as inadvertently 

 stated on p. 29 of "Land and Fresh-Water Shells," I. 



The distribution of the genus is world-wide. 



Fig. 15. Fig. 16. Fig. 17. 



Jaw of Z. arboreus (Morse), Jaw of Z. /uliginosus. Jaw of Z. indentattu (Morse). 



The jaw of Zonites is arcuate, ends acuminated, often recurved, sometimes 

 blunt ; anterior surface without ribs ; cutting margin with a beak-like pro- 

 jection. 



I have examined the jaws of almost all of our species. There is con- 

 siderable variation in their form, but the general characters are constant. 

 Sometimes there is a vertical median carina, as in Z. minusculus. Some species 

 have vertical striae, especially on the middle of the jaw (Fig. 15). Some have 

 strong transverse lines of reinforcement (Fig. 16). In several species, such 

 as Z. viridulus and Z. Binneyanus, Morse has detected projecting points on the 

 cutting edge of the side of the median beak, but I did not find them in a 

 specimen of the last species examined by me. The jaw of this last species 

 is very high. That of Z. exiguus is very low. The median vertical grooves 

 in some species are mentioned below (^Z.ferreus). 



In the preceding genus Glandina we found only the aculeate form of teeth 

 or pure marginals ; in Macrocyclis we found, in addition to these marginals, a 

 few teeth showing a modification of this type, being the transition teeth from 

 marginals into laterals. In the present genus, Zonites, we find for the first 

 time the lateral teeth in their full development. Thus we have usually the 



Fis. 18. 



General View of Dentition of /.omtes arboreus. 



three forms of teeth — centrals, laterals, and marginals — all present, and appar- 

 ently a generic characteristic. It will be noticed, however, that in Icevigatus ^ 



1 See also Z. cellar ius. 



