572 ON THE GEOGRAPHICAL DISTRIBUTION 



animal so marked is possibly not indigenous, was removed from the 

 Limax agrestis, and prefixed to the curious name 'Arion fuecus, 

 Miill/ 



It is difficult to understand how the late Dr. O. A. L. Morch can 

 have come, in 1875, to alter his previous entry in this manner. 

 For the name ' Arion ' was unknown to Miiller, the author of the 

 *Historia Vermium/ having been introduced into malacology by 

 Ferussac, as he himself tells us ^ ; and as regards the animal itself, 

 on the supposition that Dr. Morch, by his entry ' Arioft fuscus, 

 Miill.,' intended to have written ' Litnax fuscus, Miill. ;' and 

 knowing that this Limax_, so called by Miiller, was really an Arion 

 (kortefisis), and not a slug with a posteriorly placed respiratory inlet 

 and a continuous shell, it is still more difficult to see how he could 

 have added the word Jj. agrestis, L., apparently as a synonym. 

 For in the thirteenth edition of the ' Systema Naturae,' tom. i. 

 pars vi. pp. 3101-3102, the (true) ' Limax agrestis ' is distinguished 

 from the ^ Limax fuscus^ [=Ario7i liortensis hodie) of 'Miiller, Hist. 

 Verm. ii. p. ii. n. (^09.' 



On referring to Dr. O. A. L. Mcirch^s * Faunula Molluscorum 

 Islandiae,' communicated on the 13th April 1866, and published 

 in 1868, in Danish, in the 'Vidensk. Medd. fra den naturhist. 

 Forening i. Kbvn,' pp. \^^-%2^, I find at p. 196, 3, that '•Limax 

 agrestis, L.' stands with a ? after its name, even though there can 

 be no doubt from references to Olafsen, several of which are, in 

 fact, given by Morch, that a gray slug, as well as the black slug, 

 Arion ater, exists in Iceland. And a suggestion at the end of the 

 entry, to the effect that the specimens may possibly belong to the 

 species Limax tenellus, appears to explain the presence at the 

 beginning of it of a ? after the words Limax agrestis. 



Perhaps, therefore, the true explanation of the entry in the 

 Manual of 1875 ^^ ^^ follows. In the interval between 1857 and 

 1875 a black slug may have been proved to Dr. Morch's satisfaction 

 to have been found in Greenland, and he may have identified it as 

 the Arion fuscus of Moquin-Tandon, which is the same as the Arion 

 hortensis of Ferussac, and as the Limax fuscus of Miiller and 

 Linnaeus ; and he may, by a very slight slip, have entered it as 

 ^ Arion fuscus, Miill.,' instead of * Arion fuscus, Moquin-Tandon,' or 

 * Limax fuscus, Miill.' To his addition ' Probably introduced,' 



* 'Hist. Nat. des Mollusques,' ii. 1820-1851, pp. 23 and 54. 



