140 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



are arranged in straight transverse rows, the marginals in oblique rows, as acu- 

 leate marginal teeth always are. This tendency to obliquity in the rows of 

 aculeate teeth we have seen most plainly shown in Glandina.- To show the 

 general arrangement of the teeth in straight and oblique rows I repeat the fig- 

 ure by Morse in " Land and Fresh- Water Shells, N. A." I., which was probably 

 drawn from L. agrestis. It must be borne in mind that this figure is not intended 

 to show the characters of the separate teeth, for which I refer to my plate. 



The genus Limax differs from Zonites in its dentition by having more slen- 

 der, 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 irregularly 'circular on the extreme marginals. Another difference i s 



Fig 56. 



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 de- 

 crease gradually in size from the first to the last. It is the same with agreslis, 

 but I believe the character is not generic, as L. montanus differs in this respect. 

 It will be seen that even in the few species existing in North America there 

 is considerable variation in the lingual dentition, especially in the bifurcation or 

 non-bifurcation of the marginal teeth, the development of the side cusps to the 

 central and lateral teeth, and the presence or absence of distinct cutting points 

 to these cusps. I shall, however, simply describe the dentition of our species, 

 without reference to the subgeneric or generic value of these differences of 

 dentition, or of the peculiarities of the mantle on which also generic and sub- 

 generic distinctions have been founded. 



Species of Limax have been found in every quarter of the globe, but they 

 may be said to belong rather to the more temperate regions. In North Amer- 

 ica they are less common in the tertiary portions of the Southern States, but 

 are found abundantly in the Middle and Northern States and in the British 

 Possessions. Specimens were collected by Mr. Kennicott as far north as the 

 junction of the Yukon and Porcupine Rivers in Russian America. The 

 Pacific States also are inhabited by several species. I have received one from 

 Lower California. The genus is also found in the Central Province. The 

 cellars and gardens of the cities of the Atlantic seaboard are infested with sev- 

 eral European species, introduced by commerce. Like rats and mice, and vari- 

 ous destructive insects which have proceeded from continent to continent and 



