XVI INTRODUCTION. 



Ill the "Medical Repository" for 1821, Dr. J. E. Gray described a second 

 species of Avion as an inhabitant of this country : 



6. Arion hortensis. 



In 1823 Sowerby published his " Genera of Recent and Fossil Shells," 

 iu which he described a second species of Testcicella : 



7. Testaeella seutulum. 



This, however, after the issue of Turton's Manual of 1831 was regarded as 

 hut a slight variety of T. haliotiden, and consequently disappeared from 

 our lists as a species. 



In the same year, 1823, F6russac described from British examples the 

 first of our two species of keeled slugs : 



8. Milax sowerbii. 



Meanwhile, various faunal works on niollusca had been issued by 

 Da Costa, Donovan, Montagu, Maton and Racltett, and others, in which 

 the slugs were not included, but in 1828 the Rev. John Fleming published 

 liis " History of British Animals," in which we find the first description as 

 British of the third species of Testaeella : 



9. Testaeella haliotidea. 



In the same year. Dr. George Johnston, in a paper criticizing Fleming's 

 work, described a third species oi Arion : 



10. Arion circumscriptus. 



This species, however, never afterwards appeared in our lists and manuals, 

 other than as a synonym or variety of ^1. hortensis, or as the supposed 

 young of J. afer, 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 Arions, which, having no distinct 

 shell, found no definite place in a work devoted to testaceous niollusca. 



In 1832 and 1833 Mr. John Denson published detailed and elaborate 

 accounts of Mila.r sowerbii and Testaeella seutulum in the " Magazine of 

 Natural Hi.story," and in is;!7 Mr. Thomas Nunneley published iu the 

 Leeds Transactions a detailed account with figures of the anatomical 

 structure of the first four British species, describing therein the intestinal 

 appendix oi Limax Jlavus, 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 tlie subject. 



In 183K Dr. George Johnston brought forward in his Berwickshire list 

 aiioilier species : 



11. Agriolimax Isevis, 



