XVl INTRODUCTION. 
In the “‘ Medical Repository” for 1821, Dr. J. E. Gray described a second 
species of Arion as an inhabitant of this country : 
6. Arion hortensis. 
In 1823 Sowerby published his “ Genera of Recent and Fossil Shells,” 
in which he described a second species of Testaucella : 
7. Testacella scutulum. 
‘This, however, after the issue of 'urton’s Manual of 1831 was regarded as 
but a slight variety of 7. haliotidea, and consequently disappeared from 
our lists as a species. 
In the same year, 1823, Férussae described from British examples the 
first of our two species of keeled slugs : 
8. Milax sowerbii. 
Meanwhile, various faunal works on mollusea had been issued by 
Da Costa, Donovan, Montagu, Maton and Rackett, and others, in which 
the slugs were not included, but in 1828 the Rev. John Fleming published 
his “ History of British Animals,” in which we find the first description as 
British of the third species of Testacella : 
9. Testacella haliotidea. 
In the same year, Dr. George Johnston, in a paper criticizing Fleming’s 
work, described a third species of Avion : 
10. Arion cireumscriptus. 
This species, however, never afterwards appeared in our lists and manuals, 
other than as a synonym or variety of A. hortensis, or as the supposed 
young of A. ater, even by Johnston himself, and was only finally re-estab- 
lished as of true specific rank fifty-eight years afterwards. 
'Turton’s Manual, published in 1831, was the first to bring all these 
species together in one work, except the Avions, which, having no distinct 
shell, found no definite place in a work devoted to testaceous mollusea. 
In 1832 and 1833 Mr. John Denson published detailed and elaborate 
accounts of Milax sowerbii and Testacella scutulum in the “ Magazine of 
Natural History,” and in 1837 Mr. Thomas Nunneley published in the 
Leeds ‘Transactions a detailed account with figures of the anatomical 
structure of the first four British species, describing therein the intestinal 
appendix of Limae flavus, and his careful and accurate work, the first 
molluscan anatomy after Lister’s, foreshadowed the closer attention paid 
in late years to this branch of the subject. 
In 1838 Dr. George Johnston brought forward in his Berwickshire list 
another species : 
11. Agriolimax levis, 
