NATURAL SCIENCES OF PHILADELPHIA. Wey 
ing more slender, spine-like marginals, instead of the short, 
strictly aculeate form. The base of attachment of the marginals 
in Limazx is also different, being less sole-like, and more irregu- 
larly circular on the extreme marginals. Another difference is 
Fig. 18. 
Lingual dentition of Limaz. 
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 LZ. 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 A. 
In grouping the genera of Helicinx, 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 PATULA, 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, 
Jaw of Patula asteriscus. [Morse.] Jaw of Patula striatella. [Morse.] Jaw of P. 
} alternata. 
however, such as strigosa and Cooper, there are distinct traces of 
