North American Species of Zonites, etc. 359 



Z. lasmodon, it has fully 8 whorls, is 6§ mill, in diameter, the 

 umbilicus 1 mill, wide, whilst lasmodon with 7 whorls is 7 mill, 

 in diameter, with an umbilicus 2 mill wide : the Eoan Mountain 

 shell has also five parallel lamellae, while lasmodon has only two, 

 or at most three, and does not show the successive rows of lamel- 

 lae which are characteristic of Andrewsi, radiating from the 

 centre. 



From Z. significans it differs in its larger size, greater number 

 of whorls, much wider umbilicus, and in the character of its 

 internal denticles, which are long and winding on the wall of the 

 whorl ; while in significans the denticles are simply erect and 

 conical, with broad base. The same differences distinguish it 

 from multidentatus, which is still smaller than significans, and 

 has a much narrower umbilicus. 



Zonites macilentus, Slmttl. 



On pi. X\ f , fig. B, I give an illustration of what appears to 

 be the true macilentus (see Terr. Moll., Ill, p. 20), which seems 

 to be distinct from lasmodon, judging by specimens lately re- 

 ceived. 



For the sake of comparison with Z. significans and allied 

 sj)ecies, I give on pi. XV, fig. F, an enlarged view of this 

 species, more satisfactory than that given in Terr. Moll-. IT. S., 

 III. 



Zoniles significans, Bl. 



By an unfortunate oversight, another shell was used to illus- 

 trate this species in Terr. Moll., V, p. 132. I here figure (pi. 

 XV, fig. G) an authentic specimen. 



On pi. XIV, fig. F, I have given, for the sake of comparison, 

 an illustration of Z. multidentatus, the nearly allied species. 



Zonites cuspidatus, Lewis. 



In the Proceedings of the Academy of Natural Sciences of 

 Philadelphia, 1875, p. 334, this is mentioned as probably a var. 

 oi'Z. cerinoideus. I have received authentic specimens from 



