256 



ZOOLOGY. 



Subclass II. Euthyneura (Land Snails and many naked Mollusks). 

 Gasteropods in which the nerve loop is not twisted. The head usually 

 bears two pairs of tentacles. The sexes are united in the same individual. 

 The most important of these are the Pulmonata or air breathing Gastero- 

 pods, some of which are terrestrial and others aquatic. Of the terrestrial 

 snails the genus Helix (Fig. 119) is the most widely distributed and inter- 

 esting. Its variability is such that between three and four thousand 



FIG. 118. 



FIG. 119. 



FIG. 118. Acma-a testudinalis (Limpet), from Binney's Gould. Upper figure lateral 

 view; lower figure, dorsal view. 



Questions on the figure. How do the Limpets differ from the ma- 

 jority of the snails? What is the appropriateness of the specific name 

 (testudinalis') ? 



FIG. 119. Helix albolabris, a pulmonate Gasteropod. From Binney's Gould. 



Questions on the figure. What is the significance of Helix? Of 

 albolabris ? Identify the parts of the shell. Is it a right or left spiral? 

 What do you mean by your answer? 



FIG. 1 20. 



FIG. 120. Limax flai'us, a Slug. From Binney's Gould. 



Questions on the figure. How do the slugs differ from the other 

 Gasteropods? In what external respects do they appear similar to them? 

 Compare all the figures of slugs you may be able to find. 



