58 COLLINGE : REVIEW OF THE ARIONIDyE OF THE BRITISH ISLES. 



Sub-family ARION IN. K. 



1. Arion, Fer. 1819. 6. Prophysaon,B\6.k.'Bmx\. 1873. 



2. Ariunculus, Lessona. 1881. 7. Anadenulus, Ckll. 1S90. 



3. Geomalacus, Allman., 1846. *8. Hesperarion, Simroth. 1892. 



Letourneuxia, Bgt. 1866. 



4. Anadcnus, Heyne. 1863. [9. Tetraspis, Hagenm. 1885]. 



5. Ariolimax, Morch. i860. [10. Aspidoporus, Fitz. 1833.]. 



Genus Arion, Ferussac, 18 19. 

 Body nearly cylindrical, elongated, strongly wrinkled ; mantle 

 shagreened or granulate ; tentacles separated at their base : 

 respiratory orifice in front of middle of right edge of mantle ; 

 genital orifice below and close to respiratory orifice ; keel 

 absent, a slight indication of one in young forms; mucous gland 

 at posterior extremity of body, triangular, base of angle directed 

 towards the head ; shell consists of loose calcareous granules in 

 some species, in others, however, they assume a more compact 

 form. Subject to great variation. 

 This genus was created by Ferussac in 18 19. It is confined to 

 the European region, with the exception of those introduced by 

 human agency into North America, New Zealand, St. Helena, &c. 

 There are nine species known to the British Isles.t 



Moquin-Tandon has divided the genus into two sub-genera : 

 Lochea and Prolepis. In the former the shell is represented by a 

 series of unequal, isolated, calcareous granulations, and in the latter 

 by an aggregation of separate calcareous particles. Simroth (39) 

 divides the genus into Monatriidce and Diatriidcc, according to the 

 number of vestibules. Pollonera (31) classes the various species, <Scc, 

 under four groups as follows : — 



1. The A. evipiricorum group. 3. The A. Jiortensis group. 



2. The A. sitbfuscus group. 4. The A. bour°ui«nati group. 

 The anatomy has been carefully described by Nunneley (28), 



and still later by Simroth (39), and that of various species by 

 Lawson (22a) and Pollonera (29, 30, and 31). I shall, therefore, 

 point out only the principal characters. There are four convolutions 

 of the intestine, thus being easily distinguished from Liinax, which 

 has six. There are two tentacular muscles, which arise indepen- 

 dently, and supply the upper and lower tentacles — from the latter a 

 small labial branch is given off. The pharynx retractor muscle arises 

 beneath the mantle on the left side of the body wall ; it divides into 



* Created since Mr. Cockerell's paper was written. 



t I am ranking all the forms mentioned here as species, as I have previously done in my 

 '• Catalogue of British Slugs." It is quite possible, however, that some may ultimately be shown 

 to be but sub-species. 



