NATURAL SCIENCES OF PHILADELPHIA. 



m 



ing more slender, spine-like marginals, instead of the short, 

 strictly aculeate form. The base of attachment of the marginals 

 in Limax is also different, being less sole-like, and more irregu- 

 larly circular on the extreme marginals. Another difference is 



Fig. 18. 



Lingual dentition of Limax. 



that the marginal teeth do not increase in size so rapidly, and 

 then decrease gradually as they pass off laterally, thus giving an 

 irregularly crescentic form to each half of every transverse row. 

 In L. maximus the marginal teeth decrease gradually in size from 

 the first to the last. It is the same with agrestis, and I believe 

 the character to be generic. 



b. Jaw in one single piece, marginal teeth quadrate. Helicin^e. 



In grouping the genera of Helicinse, I have placed (1) those 

 whose jaw has no distinct ribs upon its anterior surface; (2) 

 those whose jaw has decided stout vertical anterior ribs; (3) 

 those whose jaw has delicate, distant ribs generally running ob- 

 liquely towards the median line of the jaw. 



(1) Jaw without decided ribs on its anterior surface. 



Genus PATTJLA, Held. 



In none of the American species of this genus have I found a 

 jaw with distinct well-formed ribs as in Helix. In several species, 



Fig. 19. 



Fig. 20. 



Fig. 21. 



Jaw of P. 

 alternate/,. 



Jaw of Patula asteriscus. [Morse.] Jaw of Patulu striatella. [Morse.] 



however, such as strigosa and Cooperi, there are distinct traces of 



