446 m:e, w. e. collistge on etjbopean slugs. [May 4, 



certainly not sufficient to constitute either a new genus or sub- 

 genus. 



In 1870 Mabille (16) gave the Arion fasciatus group, mentioned 

 on p. 447 in this article, the name of Caritiella, under the impression 

 that all the species were keeled, which, however, is not the case, 

 as I have elsewhere pointed out (6). Seibert in 1873 (Xachr. 

 malak. Gesell. A'oI. v. p. 81) proposed the name KoJheltia for the 

 A. Jiortensis group. Later Simroth (32), 18S5, divided the genus 

 into two sections, the Monatriidce and Diatriidce. In the former 

 division all species possessing a single vestibule were gi'ouped, and 

 in the latter all those in which the oviduct before opening into the 

 lower vestibule dilates, thus forming as it were a second vestibule. 

 Pollonera (19), 1887, has ^ery clearly shown that such a character 

 as the presence of either one or two vestibules cannot serve as 

 a basis for classification, it not being a feature of sufficient 

 importance. Further, he thinks that Simroth attached too much 

 importance to such a character, through his having limited his 

 study to the few Germanic forms. Pollonera showed that we not 

 only find in the same groups species which are Monatriidce and 

 species which are Diatriida-, but also that in the four groups into 

 which he has divided A. Jiorfensis two s|)ecies are Diatriidce 

 (A. hortensis and A. celficus) and two are Monatriidoi {A. alpinus 

 and A. nilssoni) ; further the A. havayi belongs to the so-called 

 Monatriidce, while ^4. rufus and A. ater are the two species in Avhich 

 the -Diatriidce condition is most marked. In a later paper (21) this 

 distinguished malacologist points out that the A. hortensis from the 

 Xorth of France are all Monatriidce, whereas those from Germany 

 are Diatriidce, while those from the East of France are inter- 

 mediate between tlie two. From these facts I think it will be evident 

 that we can no longer separate the members of the genus Arion by 

 the number of vestibules they possess into subgenera, groups, &c. 

 The character is interesting and may possibly be of service in 

 separating species, but as a feature for generic distinctions is 

 useless. 



Pollonera has suggested (19) the division of the genus into four 

 groups, viz. : — 



1. The Arion empiricorum group. 



2. The Aj-ion stdifusciis group. 



3. The Arion hortensis group. 



4. The Arion hourguignaii group. 



I think this suggestion preferable to any yet proposed, and it is 

 the one I have here followed, with some slight alterations, as 

 shown in the following synopsis of the genus. 



Synopsis of the Genus Asion. 

 1. The Arion ater geotjp '. 

 The animal is large and unicolour in the adult. Earely banded 



' I use the name ater for this group, as it is an older species than A. empiri- 

 corum. 



