SOME OBSERVATIONS ON CERTAIN 

 SPECIES OF ARION. 



By WALTER E. COLLINGE, F.Z.S. 



(Assistant-Lcctuvcy and Demonstrator in Zoology and Comparative Anatomy, 

 Mason College, Birmingham.) 



{PLATE II.) 



I have recently received a large series of living examples of 

 A. ater, L., A. rufiis, L., A. cmpiviconim, Fer., and A. lusitamcus, 

 Mabille, and knowing the very divided opinion that exists amongst 

 malacologists as to the specific validity of these four forms, I 

 have submitted them to a very careful examination, with the 

 following results : — 



I. Arion ater, Linne, 1746. (PL II., Fig. i.) 



Externally this species is very like A. cinpivicoyuni, Fer., the 

 differences being very minute and unimportant. All the speci- 

 mens I have seen, however, have been much larger than A. 

 empiricoynm ; thus in twenty adult specimens, the length was as 

 detailed below, the maximum being 125 millim., whereas of forty 

 adult specimens of A. empivicorum, the maximum length was 

 118 millim. 



Arion ater. Arion empiricorum. 



5 Specimens .. 110-115 millim. 15 Specimens .. 80- 90 millim. 



8 ,, .. 120 ,,' 12 ,, .. 90-100 



7 .. •• 125 ,, 10 ,, .. 115 



5 „ .. iiS 



All the specimens were measured while alive. The internal 

 differences in the form of the terminal portions of the generative 

 organ=; are much more distinct. There is only a single vestibule 

 — the lower one. The sperm-duct opens at the junction of the 

 vestibule with the lower terminal swelling of the free-oviduct. 



