I9S 



ARION SUBFUSCUS. 



the body are nearly black ; this greater uniformity is naturally to be ex- 

 pected, as A. suhfuscus is a more ancient species and not a dominant form. 

 The junction of its distribution with the limits of the more restricted 

 area inhabited by A. atei; is complicated in those districts by the external 

 approximation in aspect of the two species, a resemblance which has been 

 the cause of great confusion, as many authors have, at various times, 

 recorded the present species under one or other of the different names of 

 its larger congener. 



On the Finnish shores of the Gulf of Finland, the var. fennica assimilates 

 in a very remarkable way to Avion ater, under which name it has frequently 

 been recorded; while the Avion lusitanicus, A. nobvei, and A. dasihae, 

 which have been described from the Spanish peninsula, are undoubtedly 

 intermediate forms linking suhfuscus with atev, r&semhlmg suhfuscus in their 

 internal structure but often approximating externally more closely to ater 

 especially in size and colouring. 



The Avion flagellus of Collinge, which is 

 here regarded as a simple variety oi A. suh- 

 fuscus, is said to possess as its characteristic 

 feature a distinct flagellum upon the free 

 oviduct, a most improbable situation for such 

 an organ ; but, as the illustrative figures of 

 the author are somewhat carelessly or inaccu- 

 rately executed, it is quite possible that the 

 proposed species has been presented under a 

 misapprehension of the precise structure of 

 the animal. 



The yellow colouring of the body, though 

 in general due to the mucous investment, is 

 not invariably so, as in some cases the colour- 

 ing is really due to the breaking through the 

 skin of the superficially placed colour glands. 



The yellow dermal mucus, though so char- 

 acteristic a feature, is also not an invariable 

 trait of this species, as the darker and also 

 the more pallid varieties more frequently 

 emit an almost colourless slime. 



Avion suhfuscus, like Limax c(,vhorum and 

 Ai'ion atev, offers, according to Simroth, the 

 same striking evidence of the darkening in- 

 fluence of altitude, as the individuals inhab- 

 iting the lofty mountain ranges are invariably 

 darker than those living on the plains below. 



On the contrary. Dr. Scharff expresses the opinion that in Ireland the 

 more or less unicolorous pale yellow variety is more especially characteristic 

 of the higher parts of the countiy while the darker typical form inhabits 

 , the plains. 



VARIATIONS IN COLOUR AND MARKINGS OF ANIMAL. 



Var. rufo-fusca Draparnaud, Hist. Moll., 1805, p. 125. 



Avion cincius var. rttfescens Duin. & MorL, Moll. Savoie, 1857, p. 7. 

 Avion rvbiginosus Baudon in Drouet, Moll. C6te d'Or, 1868, p. 26. 

 Avion gnudefvoyi Mabille, Hist. Moll. P.iris, 1870, p. 12. 



Animal of a lufoii.f tint, most pronounced on the mantle and the sides of the 

 liody, dor.Huiii darker, the lateral band black or blackish. 



'i'liis form in the one selected by Diapaniand as the tyjie of the .species; but tlie 

 vnfous colouring is in many cases entirely due to tlie mucous investment. 



Fig. 219. — Reproductive Organs 

 of Avion flagellus Collinge (after 

 Collinge). The ovispermatoduct is 

 incorrectly represented, and some of 

 the _ organs wrongly identified in 

 Collinge's original figure. The figure 

 is, however, here given as in the 

 original, but the nomenclature of the 

 organs is corrected. 



a.g. albumen gland ; a. atrium ; 

 ep. epiphallus \fl. flagellum ; h.d. her- 

 maphrodite duct ; ot. ovotestis ; o^i. 

 oviduct ; 07/ , free oviduct ; v.vi. re- 

 tractor muscle ; s.d. sperm duct or 

 prostate ; sp, spermatheca ; v.d. vas 

 deferens. 



