NATURAL SCIENCES OF PHILADELPHIA. 



171 



Fig. 15. 



Zonites and Hyalina, respectively characterized by the presence or 

 absence of a distinct locomotive disk to the foot, 

 and well-marked furrows running above, and 

 parallel to, the edge of the foot, meeting above 

 the extremity of the tail over a distinct caudal 

 mucous pore (fig. 15). I now place them all in 

 Zonites, as all I have examined are so charac- 

 terized, and I believe all will prove to be so. (See Ann. N. Y. 

 Lye. N. H., X. 164.)' 



The external orifice of the generative organs in the species I 

 have examined is quite under the mantle, not on the right side of 

 the head, as inadvertently stated on p. 29 of L. and Frw. Shells, I. 



Tail of Zonites 

 suppressus, enlarged 



Genus VITRINA, Drap. 



To the description of the animal on p. 29 of L. and Frw. Sh.N. 

 A., I., must be added the fact of there being a distinct locomotive 

 disk to the foot. 



Fig. 16. 



Lingual dentition of V. limpida. [Morse.] 



The jaw is highly arched, ends acuminated, blunt ; anterior sur- 

 face smooth ; cutting margin with a prominent beak-like median 

 projection. I have figured the jaw of V. limpida on pi. XVI., fig. 

 3. I have found it to be the same in V. exilis and Pfeifferi. I 

 have not examined either jaw or lingual membrane in V. Angelicas. 

 Fig. 16 gives a general idea of the lingual membrane. The cen- 

 trals have a quadrangular base of attachment, longer than broad: 



' I have also observed the caudal pore in limatulus. Z. arboreus has the 

 longitudinal furrows, but on account of the transparent tissue of the foot I 

 find it difficult to distinguish any caudal pore. 



In Z. ligerus there are well-marked lines running obliquely towards the 

 centre of the base of the foot, where is an extremely narrow T line,. repre- 

 senting, no doubt, the locomotive disk. The other characters of Zonites 

 are present in the species. 



