HARDWICKE'S SCIENCE-GOSSIP. 



255 



THE ENDEMIC FEATURES OF THE 

 BRITISH SLUG-FAUNA. 



By T. D. A. COCKERELL. F.Z.S., F.E.S. 



DR. A. R. WALLACE, in " Island Life " (2nd 

 ed., Part ii., chap, xvi.) gives a very interest- 

 ing discussion of the British fauna and flora, in 

 which he argues, contrary to the opinion of many, 

 that there really are numerous species and varieties in 

 our islands which are truly peculiar to them, either 

 having arisen within our area, or else been formerly 

 more widely distributed, but now surviving only in 

 Britain. 



In discussing a question of this kind, we need very 

 full information as to the foreign species and varieties, 

 and this, unfortunately, is not usually in the posses- 

 sion of British students ; while foreigners, as a rule, 

 are not well-acquainted with our supposed endemic 

 forms. It happens, however, that of late years the 

 slugs and their variations have received special 

 attention at the hands of several naturalists, and 

 some very full and elaborate works have appeared, 

 giving us much of the desired information. The 

 slugs, also, being extremely prone to vary, and slow 

 to migrate, are specially suitable for illustrating the 

 points at issue. 



The following notes have accordingly been put to- 

 gether, constituting an examination of the forty-four 

 varieties and mutations which have been first de- 

 scribed from British specimens. There are a few 

 still unnamed forms not mentioned, as it seems best, 

 for purposes of comparison, to include only those 

 which have been named and listed. It seems un- 

 necessary to give full bibliographical references ; but 

 it may be remarked that no names are herein pub- 

 lished for the first time. 



The objection is almost sure to be raised, that 

 many of the forms are of no interest, being merely 

 individual mutations. From the view that such are 

 unimportant, I entirely dissent ; and it may be 

 pointed out, that such mutations are very frequently, 

 perhaps more often than not, restricted to one 

 portion of the range of the species. Take for 

 example the var. albolateralis of Arion ater. Over 

 the greater part of the range of the species it does 

 .not occur at all ; in parts of Britain it is a rare 

 aberration or mutation, while in certain districts it 

 becomes a distinct and common variety. So also 

 with Agriolimax agrestis, var. niger, and many 

 others. It is the greatest mistake to suppose that any 

 species shows the same kind and amount of vari- 

 ability in every part of its range, unless, indeed, that 

 range is extremely limited. 



Testacella (Cuv.). 

 i. T. scutulum, mut. pallida, Ckll., pale yellow 

 without markings. Chiswick, with the next. A 

 similar mutation (flavescens, Moq.) of T. haliotidea is 

 known on the continent. 



2. T. scutulum, mut. aurea, Ckll., mottled with 

 brown, but the sole vivid orange. 71 bisulcata, 

 Risso, which differs hardly at all from scutulum, 

 varies towards orange in France. T. maugci has a 

 variety (viridans, Morelet) with a brilliant orange 

 foot, found in Portugal and, according to Mr. Roe- 

 buck, in Co. Waterford, Ireland. 



Limax (L.). 



3. L. maximus, mut. lilacinus, Roeb. Like mut. 

 kiynickii Kal., as to markings, but the ground-colour 

 clear lilac. Found at Stroud, Gloucestershire. 

 Interesting, as showing a tendency towards the 

 brighter colours observed in the same species further 

 south. Baudon records a variety vinosa from France ; 

 and the reddish var. rufescens, Moq., first described 

 from France, has been taken in Britain. Agriolimax 

 agrestis varies in a similar way, from the grey type, to 

 reddish (mut. rufescens, L. and P.) and violaceous 

 (mut. lilacinus, Moq.) forms, both of which occur in 

 England as well as on the continent ; the latter is found 

 in the same district as the lilac form of L. maximus. 



4. L. maximus, mut. cinereus, Roeb. (non Moq.). 

 This is ashy, unicolorous, with the mantle blackish, 

 and is reported from various localities, including four 

 Scottish counties (Roebuck). It was supposed to be 

 the same as var. cinereus of Moquin-Tandon (1855), 

 but that is equivalent to Midler's cinereus, var. a, 

 which is doubtless L. cinereo-niger. Ferussac 

 ("Hist. Nat. Moll.," PI. iv. f. 1 ) figured this same 

 cinereus, var. a, as is noticed by Moquin-Tandon ; 

 and the vzr.Jentssac&ii (sic) of Kaleniczenko (1S51), 

 was intended to include the form depicted by 

 Ferussac* 



The British form of L. maximus, which has been 

 called cinereus, probably does not differ from 

 similarly-coloured slugs which occur on the continent. 

 O. F. Mtiller ("Verm. Hist." 1774. vol. ii. p. 7) 

 described a variety as ashy, with a white border and 

 sole ; this, in 1855, was named limbatus by Moquin- 

 Tandon. Heynemann (" Mai. Blatt.," 1862, p. 55) 

 gave the name unicolor to an almost identical form, 

 which is now known from Germany, Italy, and 

 Sicily. Lessonaand Pollonera (" Mon. Limac. Ital.," 

 1882) call it a species, L. unicolor, with four 

 varieties. These are really all suffused or melanic 

 forms, such as occur in many species of slugs. With 

 the same group, but less melanic, are the mutations 

 known as obscurus, Moq., and nebulosus, D. and M. ; 

 these are both British and continental. 



5. L. maximus, mut. marmoratus, Ckll. Found 

 at Chislehurst, Chiswick, and Bath ; closely allied to 

 mut. krynickii, but the mantle is beautifully marbled, 



* Kaleniczenko's razoumowskii and renardii, described as 

 varieties of L. antiquorujn, are also forms of L. cinereo-niger ; 

 but his czemarvii and krynickii belong to L. maximus. The 

 var. czernavii may be taken as equivalent to Moquin-Tandon's 

 vulgaris, over which it has priority, although it was intended 

 to include forms now referred to cellarius as well. Fasciatus, 

 Pic. (T840), a still earlier name for the same, must apparently 

 fall, as there is a different mut. fasciatus, Raz. (1789}. 



