1897. J ME. W. E. COLLIiSTGE OX EUEOPfiA-N SLUGS. 447 



or striped, excepting in young specimens. Mantle large. Adult 

 never keeled. Free-oviduct of moderate length, with its terminal 

 portion usually globose or expanded. Sperm-duct usually, but 

 not always, opens into the vestibule by a thickened ring-like 

 swelling. Retractor muscle of the free-oviduct always situated 

 above the lower portion, and joins with that supplying the 

 receptaculum seminis. 



2. The Arion suhfuscus group. 



Usually banded, variable in colour. Varies in size from 35 to 

 75 millim. Mantle rather large. Adult never keeled. Free- 

 oviduct generally sac-like or wide and long, without well-defined 

 terminal swelling. Duct of receptaculum seminis usually long. 

 Eetraetor muscles of the free-oviduct and receptaculum seminis 

 usually distinct or only slenderly united. 



3. The Arion liortensis group. 



Nearly always banded, of dark colour. Varies in size from 

 30 to 55 millim. Mantle medium-sized, often small. Adult never 

 keeled. Sperm-duct usually long and tapering, passing imper- 

 ceptibly into the vas deferens. Free-oviduct gradually tapering. 

 Retractor muscles usually united, but only slenderly. 



4. The Arion fasciatus group. 



Nearly always banded. In external appearance agrees very 

 closely with the preceding group. Body sometimes keeled. Head 

 of receptaculum seminis elongated, duct short. 



5. The Arion intermeditts group. 



Animal usually of small size, varying from 15 to 27 millim. 

 Mantle almost circular. Adult never keeled. Eeceptacular duct 

 short and broad. 



Lessona and Pollonera (14) are wrong in stating, as one of the 

 characters of the genus, that the penis ( = sperm-duct) and Tas 

 deferens are quite distinct, and do not pass imperceptibly into 

 one another as in Ariunadus, for in numerous species there is no 

 marked difference between the two. 



The term penis cannot be used for the male organ in this genus ; 

 as has been pointed out by Simroth, it is not evertible, and has 

 no retractor muscle, its function being for the storage of the 

 spermatojoa. The free-oviduct assumes the function of the penis 

 in this genus. It is evertible and provided with a retractor 

 muscle. Messrs. Pilsbry and Vanatta (18) have suggested the 

 term epiphallus for what I term sperm-duct, and vagina for what 

 I term free-oviduct. 1 think it preferable, however, to retain 

 the term epiphallus for the terminal portion of the vas deferens 

 above the sperm- duct; the term vagina is not applicable to the 

 genus Arion. 



30* 



