78 collinge: a review of the arionid/e of the British isles. 



Ario?i marginatus, Kickx, Bull. Acad. Roy. Sci. d. Bruxelles, T. iv, 

 p. 139, 1837. 

 ,, leucophceus, Normand, Descr. six limaces nouv., p. 6, 1852 



(description insufficient). 

 ., hortensis, var. grisea, Bourg., Make. Gr. de Chartr., pi. i, 



fig. 10, 1864. 

 ,, dupuyanus, Bourg., Malac. Gr. de Chartr., p. 30, pi. i, 



figs. 1-4 (young examples). 

 ,, bourguignati, Mabille, Rev. et Mag. Zool., p. 138, 1868. 

 „ neustriacus, Mabille, Rev. et Mag. Zool., p. 138, 1868. 

 „ ambiguus, Pollonera, Contrib. a Studio delgi Arion europet, 

 p. 13, pi. ix, figs. 16-21, 1889. 

 Body light grey, yellow or brown ; lateral bands darker than 

 ground colour, continued to front of mantle ; head and 

 tentacles dark or greyish blue ; sole white or light yellow : 

 foot fringe greyish-white or yellow ; rugas narrow ; keel 

 variable, distinct in young specimens. 

 In introducing Nilsson's A. fasciatus as the type of a slug found 

 in this country, it will be necessary to enter in some detail into the 

 history of the same, and my reasons for classing as synonyms 

 A. circumscriptus, bourguignati, and ambiguus. In 1822 Nilsson 

 described an Arion (Limax) fasciatus, and still later used the same name 

 for very different species than his type, but this does not in any way 

 invalidate his original description. In 1828 Johnston (22) described 

 an Arion circumscriptus, which seems to have been overlooked by 

 most authors until brought to light again by Pollonera. In 1868, 

 Mabille (24) described an Arion bourguignati which Mr. Cockerell (7) 

 pointed out was the A. circumscriptus of Johnston, and in 1889 

 Pollonera described an Arion ambiguus which I am now referring to 

 A. fascia ins. 



After a careful study of an exceedingly large number of 

 specimens of all ages, I am of opinion that all the above forms are 

 synonymous with Nilsson's type. The A. circumscriptus and 

 A. ambiguus are not keeled, whereas the A. bourguignati is. In the 

 young stages A. circumscriptus exhibits slight traces of a posterior 

 keel, but the presence or absence of a keel is quite an unimportant 

 matter, as such slight external modifications — which differ greatly 

 according to age and environment — are insufficient for specific 

 distinction. 



Signor Carlo Pollonera has very kindly written me at some 

 length respecting these forms, and he is of opinion that for the 

 keeled form the name A. bourguignati, Mabille, must be retained, 

 and if A. circumscriptus, Johnst., is not keeled, he thinks we had 



