MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 103 



Genus AGIUOLIMAX M.iich. 



Tlie ftemiM Agriolinia.v or field slugs (Ager, 

 a field ; and Limi.r) was established in 

 1 S6 -, by l)r. (). A. ].. Miircli, of Copeu- 

 liageii, tlie eminent Danisli nialacologist, 

 with whom it is a pleasure to associate 

 the genus. 



The acute discernment manifested by 

 Dr. Mijrch in the institution of this genus 

 has been fully justified by the structural 

 peculiarities which further stndy has de- 

 monstrated to e.xist. 



Generic Characteristics. — The 



Agriolimaces in their typical species have 

 been shown to be quite sharply defined 

 internally and externally from the true 

 Limaces. Not only is the whole scheme of 

 coloration essentially dissimilar in so fiir 

 as there is a total aliseuce of the longi- 

 tudinal banding whicli C(jnstitutes "so 

 striking a feature in Lhna.r, but the 

 arrangement of the gut and the liver or 

 digestive gland is on quite a different 

 plan, as there are but three typical coils 

 or tracts of the intestinal canal, as in the 

 IleUcidw, all of which are imbedded 

 within the substance of the right lolie of 

 the liver, wliich in this group forms the posterior end of the viscera, 

 wliereas the left lobe occupies that position in Llmax ; the left lobe in 

 Afjrlollmux is laid obliquely in front of the crop, and is not directed back- 

 wards, as in the true Limaces. 



Contrary also to what obtains in Liniit.r, where the ingestivo or stomach 

 tract is the longest, in AgrioUmax it is the shortest of the series; further- 

 more, the male organ is free in the present genus, and not looped between 

 the retractors of the upper and lower tentacles, as in Lima.r ; the wliole 

 arrangement being thus strikingly different in the two groups. 



In addition the viscera have also retaineil a vestige of tlie pi'evious 

 prissession by the animal of a de.xtrally-coiled external shell, iu the strong 

 spiral twist to which the internal organs are subjected, a feature which has 

 become completely lost in Limax, as no evidence of a jiast tovsi(jn of tlie 

 viscera is now percei)tible. 



Geographical Distribution. — The genus Agriolimax has originated 

 witliin, and is naturally characteristic of the northern hemisjihere, its most 

 highly organized species belonging to the western pahearctic region and 

 although it is also found in other and very widel}' distant places, these 

 occurrences are probably solely due to artificial transportation. 



As we have seen in preceding groups, the more primitive or ancestral 

 species still e.xistent at the present day have, by stress of competition with 

 the more advanced forms, been expelled from the more vigorous districts, 

 and are now met with chiefly in the Mediterranean, Caucasian, and other 

 regions still more remote from their probable evolutionary area. 



