204 A MANTJAL OF AMERICAN LAND SHELLS. 



best illustrated in tlie case of Z. Iwvigatus (Plate II, Fig. F), the first 

 four side teeth being transition teeth. As already stated above, this 

 species wants entirely the perfect laterals. In Z. cellarius (Plate II, 

 Fig. G) the two transition teeth have an inner lateral spur near the top 

 of the cusp. The only lateral of this species has also peculiarities in 

 its form easily seen in the figure, but diflQcult of description. Z. inor- 

 natus (Plate II, Fig. H) has peculiar transition teeth. 



The marginal teeth of Zonites are quite like those of Qlandina and 

 MacroGyelis (see above). The curve of the transverse rows, the rapid 

 increase and gradual decrease in size as they pass off laterally, are 

 shown in Plate II, Figs. F, G, H. The number of marginal teeth in 

 each species examined is given below ; it must be borne in mind, how- 

 ever, that the number is not constant in any given species, though the 

 range of variation in number seems limited in the respective species. 

 Thus, though I have found a slight difference in the count of teeth in 

 several individuals of Z. inornatus, I have every reason to believe I 

 shall never find it to have as many teeth as in Z. fuUginosus. It ap- 

 pears, therefore, that the count of teeth has a decided specific value, at 

 least in most cases. 



The rapid increase and subsequent gradual decrease in size of the 

 teeth as they pass oft' laterally, though it appears usually a generic 

 character, is somewhat modified in some species. Thus in one lingual 

 membrane of Z. intertextus examined I find a much more gradual in- 

 crease and decrease from the first to the last marginal tooth. 



The marginal teeth in Zonites, and, indeed, all the Limacidce are more 

 separated than in the Selicidce, and the separate rows are more widely 

 removed the one from the other, especially near the outer margin of 

 the membrane. 



Though the simple aculeate form of marginals seems a generic char- 

 acter in Zonites, we find the marginals bifid in Z. fulvus (Plate II, Fig. 

 E), and bifid or even trifid in Z. Gundlachi (Plate II, Fig. D) ; also for 

 the first four marginals in milium. This character reminds us of Vi- 

 trina (see below), Vitrinoconus (Semper, Phil. Archip., 91), Vitrinoidea 

 (ibid., p. 85), vitrinopsis (ibid., p. 86), and the numerous genera of 

 disintegrated Nanina ; also some species of Limax. The first margi- 

 nals of Z. exiguus have a side spur. 



Taking the general characters of dentition into consideration, Zo- 

 nites is nearest allied to Limax among our genera, but in the latter the 

 marginals are generally more slender or spine-like and have a less sole- 

 like base of attachment. 



