XVill INTRODUCTION. 
and late in 1866, no further additions were made to our slugs or any 
notable contribution to their study for a period of nearly thirty-five years. 
‘'he present or modern period of activity in the study of our slugs 
began in 1882, when Mr. W. Denison Roebuck took up the subject as a 
special line of research, and by the active co-operation of British concho- 
logists received many thousands of slugs from all parts of the British Isles 
for examination, forming an excellent groundwork for the true appreciation 
of their distribution, variation, and developmental history. 
The late Mr. Charles Ashford, the most skilful molluscan anatomist that 
we have ever had in this country, soon became associated with Mr. Roebuck 
in the good work, and made hundreds of dissections of the various species 
and varieties, confirming the external specific characters of the various 
species by demonstrating the differences in their internal structure. 
The impetus thus given to the study was the means of bringing other 
investigators into the field, and greatly popularizing the subject. 
In Mr. Roebuck’s paper on the British slug list, published simultane- 
ously with the Conchological Society’s list of British land and freshwater 
mollusea, 1883, the specific status of 
17. Limax cinereo-niger 
was affirmed, and the name added to the British list. 
The close and systematic examination of the anatomical and morpho- 
logical character of the Arions soon showed that another species of Arion: 
18. Arion subfuscus, 
existed in this country, and although the first published notice of it as 
British was by Herr D. F. Heynemann in 1885, yet the associated labours 
of Mr. Ashford and Mr. Roebuck upon undoubted British specimens 
independently established its claim to inclusion in the British list. 
Continued investigation of the Arionide resulted in the identification 
in 1886 of Mabille’s Arion bourguignati, mainly by the aid of anatomical 
evidence. ‘The first mention of it as British was by Mr. John Emmet, 
writing on behalf of Mr. Roebuck in the “ Naturalist” for June 1886, and 
later study disclosed that the supposed new discovery was but an authori- 
tative reinstatement of Dr. Johnston’s Arion circunscriptus. 
Another resurrection made by Mr. George Roberts im 1887 and Dr. R. F. 
Scharff in 1890 was Arion intermedius. The real credit of the reimstate- 
ment, however, was due to Dr. Scharff, who showed from anatomical 
evidence that A. minimus existed with us, although in 1887 Mr. Roberts 
had given a clear description of its external morphology under the name of 
Arion flavus. Subsequent synonymic study demonstrated that these 
names referred to one and the same species, for which A. intermedius was 
the original naine. 
