May 26, 1892] 



NATURE 



77 



With regard to the peculiar species : Limmea involuta is 

 doubtless an isolated derivative of the/^/-^^rrt-type, to which 

 he curious and distinct var. burnetii of Scotland may be said 

 o lead. Assiminea firayana and Hydrohiajenkinsi belong to 

 the brackish -water and salt-marsh fauna, which, as has been 

 well observed, formerly extended far beyond its present limits. 

 To this now-restricted fauna belong many of our peculiar 

 Lepidoptera (see the list in "Island Life," pp. 347-350), and 

 the probability is that most of these are destined shortly to 

 become extinct, as the large copper butterfly {Chrysophanus 

 :ispar) already is. The fourth species, Geomalacus macttlosus, 

 Is not strictly peculiar, being also found in Portugal ; but it is a 

 survival of the Lusitanian fauna, to be classed with numerous 

 plants of similar range, recorded in "Island Life," p. 364. 

 Thus, of the four species given as peculiar, one only is strictly 

 endemic, having regard to its whole history ; and the three 

 others are apparently best regarded as survivals of faunrc which 

 were formerly more widely spread. 



Turning now to the varieties, we meet with a much larger 

 proportion of truly endemic forms, though from our want of 

 knowledge there is much uncertainty. Limax marginatus var. 

 tnaculatus is quite common in parts of Ireland, and as it is a very 

 striking form, it could not easily have been overlooked had it 

 occurred on the Continent. The same applies with perhaps greatei 

 force to the beautiful var. albolatcralis of Arion a'.er, which 

 abounds in parts of Wales. The black variety of Agriolimax 

 agrestis is frequent in some places in Yorkshire, and has never 

 been detected on the Continent. But Simroth found it 

 recently on mountains in the Azores, above the zone of cultiva- 

 tion ; and in Sicily and Creie there is a melanic form [pan- 

 orrnilanns), still more differentiated. The var. griseiis of 

 A. agrestis, found in England, and lately by Scharff in Ireland, 

 is grey instead of black, but I am not aware that even this 

 degree of melanism exists on the Continent, though, it is true, 

 they have the dark brown var. tristis. 



This melanism is well illustrated by other British slugs — 

 namely, two forms oi Limax Jlavus, znAiviooi Amaliasowerbyi, 

 and may be compared with the well-known cases of melanism so 

 frequent among our Lepidoptera. That there is a strong 

 tendency to the formation of melanic races in these islands 

 cannot, I think, be doubted ; and insular melanism elsewhere 

 has been well established as a fact. 



There is another class of varieties, noticed especially in the 

 shells, characterized by a slight and yet real difference from the 

 continental type. This sort of variation is as yet very little 

 worked out, but most conchologists who have received common 

 species in numbers from abroad, must have noticed how fre- 

 quently they have a different /^zt/Vj from those familiar to us in 

 Britain, though the actual difference may be so slight that we 

 should hesitate to separate them as varieties. Quite recently, 

 M. Bourguignat has regarded certain British specimens of 

 daiisi'ia and Unio as constituting new species. Probably 

 hardly anyone will be found to follow him in this decision, but 

 we know how thoroughly he and his colleagues have ransacked 

 Europe, and especially France, for novelties, so we may rest 

 assured that in all probability these shells represent variations 

 not existing on the Continent. 



Another class consists of forms which might be set down by 

 some as mere monstrosities, but which, nevertheless, are local in 

 their distribution. Such are sinistral forms, which occur rarely 

 in many species, but in many instances frequently in certain 

 places. This form of variation is certainly inherited, and in 

 fact has become the character of species and genera. White 

 shells of coloured species are apt to be scoffed at as mere albinos, 

 but the character is undoubtedly an important one, since in 

 Hyalinia we have every gradation of species from those which 

 rarely present white varieties, to those which are normally and 

 indeed invariably white. The colourless variety of Cochlicopa 

 Jubrica is frequent in one or two British localities, at least, but 

 I never heard of its occurrence on the C mtinent, nor in North 

 America, where the species is abundant. 



The sources of possible error, in estimating the number of 

 peculiar forms, are obviously many, and hence the need for 

 prolonged and careful research in the future. Helix virgata 

 var. subdeleta is very common in England, and I formerly 

 supposed it endemic ; but recently Mr. J. T. Carrington found 

 it at Toulon ; and Helix dautezi, Kobelt, a supposed species 

 from near Algesiras and Gibraltar, is almost precisely identical 

 with it, so far as I can judge from specimens collected by the 

 Rev. J. W. Horsley. The variety Uucozona of the same species 

 also seemed characteristic of the British fauna, but a form from 



Toulon differs but slightly from it. Arion hortensis var. fallax, 

 with orange slime, is given as peculiar. It may, however, be 

 the same as var. sufifuscus, C. Pfr., which is of a brownish 

 colour, or var. ru/escens, which is described as reddish or 

 orange. These would look extremely like fallax when the 

 latter was covered with slime ; but there is an element of un- 

 certainty, since Dr. Scharff has shown that in A. subfuscus, 

 Drap., there are two forms, one coloured reddish only by its 

 slime, as in fallax, and the other with a yellow pigment in the 

 skin. Similarly, we remain doubtful about Helix aspersa var. 

 hUescens, a form not rare in some English localities. I know 

 nothing described from the Continent that would agree with it, 

 but when it loses its epidermis it agrees with the description of 

 a French variety, and if we suppose the type of the latter to 

 have been a weathered specimen, the two must be identical. 



T. D. A. COCRERELL. 



Institute of Jamaica, Kingston, Jamaica, May 3. 



The Former Connection of Southern Continents. 



I READ Mr. Lydekker's article on "The Discovery of 

 Australian-like Mammals in South America," in Nature of 

 May 5 (p. 11), with the greatest interest. It is worth while 

 calling attention to a physiographic fact pointing towards a 

 former connection between South America and Southern Africa, 

 such as appears to be required on biological grounds, as pointed 

 out by Mr. Lydekker. 



The island of South Georgia in the Antarctic Ocean lat. 54" S., 

 long. 37° W., is composed of clay-slate, the mountains, rising 

 precipitately from the ocean, attaining to altitudes of from 2000 

 to 3000 metres (Nature, March 27, 1884, p. 509). It is about 

 1200 miles due east of Cape Horn, and almost exactly one-third 

 of the way between that cape and the Cape of Good Hope. 



The full significance of these facts seems hardly to have been 

 realized, especially from a geological point of view. The 

 existence of clay-slate rock forming mountains of an Alpine 

 character indicates with certainty that the island is a portion of 

 a submerged land of great extent. In "The Origin of Moun- 

 tain Ranges" I have dwelt upon and developed the law that 

 all great mountain ranges (not volcanoes) are thrown up only 

 in areas of great sedimentation. This is true of every mountain 

 range that has been geologically examined, and I do not know 

 of a single exception. Keeping this law well in view, clay- 

 slate mountains of an Alpine character protruding directly from 

 the ocean become invested with deep meaning. They indicate 

 vast horizontal extensions of thick sedimentary deposits which 

 have been subjected to great lateral pressure, and have become 

 ridged up along lines of least resistance. That such sedimentary 

 rocks exist far and wide, forming the ocean bottom about the 

 island of South Georgia, I have not the least doubt. A con- 

 tinental stepping-stone one-third of the way is a somewhat 

 important independent support towards the land connections 

 required by biologists between two great continents. 



Pa-k Corner, May 9. T. Mellard Reade. 



The Lesser Spotted Woodpecker. 



The lesser spotted woodpecker is rather a rare bird, and per- 

 haps the following notes may be worth recording. 



This house is in the fields, at the foot of the Cotswolds. 

 Opposite my bedroom window, and only four yards distant, there 

 is a very tall old Lombardy poplar, with a stem two feet thick. 

 One of these birds visited this tree almost every day from the 

 latter part of March till the 12th of this month, coming every 

 morning between 6 and 8, and sometimes also at other hours. 

 He fixed himself always on the same part of the stem, opposite 

 my window, and about 25 feet from the ground ; and as there 

 are only a few small branches there, he was very plainly seen 

 He made a remarkable sound, very loud, like the boring of a 

 large auger, continued for one or two seconds, and repeated 

 again and again at short intervals. While the sound continued 

 his whole body seemed in rapid vibration, and he was tapping 

 the tree with extreme rapidity with the point of his beak. 

 During the intervals his head was generally moving quickly from 

 side to side, and his beak was often turned over to plume him- 

 self. At this time the crest on his head became often a splendid 

 object. When the sun shone on it, it was like a flash of flame, 

 or the glitter of polished copper foil. The bird was about six 

 inches long, with a rather thick, fluffy-looking body, the tail 

 and back striped black and white, the stripes broadest at the 

 tail. What he was really doing I could not determine. The 



NO. 



II 78, VOL. 46I 



