ig6 



SCIENCE-GOSSIP. 



be added Fruticicola carthusiana. Characteristi- 

 cally they have thick ( x ) shells of a white 

 and black or brown colour, the white, however, 

 predominating, and occupying the whole surface 

 of the shell in F. carthusiana (-). The habitats 

 which they affect are! no less characteristic 

 than their general appearance. They are found 

 in open, dry situations, freely exposed on the 

 scanty herbage to the full blaze of the sun on a 

 hot day ( 3 ), and with little protection beyond their 

 shells to equally intense cold. It is to be supposed 

 that their pale coloration combined with their 

 thick shells is of direct physiological value in 

 withstanding the extremes of temperature to which 

 they are subjected. The whiteness enables them to 

 absorb less heat on a hot day and give out less 

 heat on a cold day ( 4 ). It must be remembered 



C 1 ) The apparently greater thickness, which is so obvious, 

 is borne out to a large extent by actual measurements. The 

 following table gives the approximate measurements of ten 

 species. The numbers are averages of a varying number of 

 specimens taken at random from those which happened to 

 be at hand. The thicknesses were measured in several 

 places on the body -whorl in each specimen, near the moutb, 

 but excluding the peristome and rib. The method of com- 

 parison in the last column is open to the objection that the 

 various species differ in shape. 



Thick- 

 Diam. Alt. ness. D xA - 

 Specie-. mm. mm. ■ mm. Th. x 10. D. x A. 



T. nemoralis ... 21 6 T&g 0-25 146 365 



T. hortensis ... 187 i4'o 021 125 262 



F.rufescens ... 123 76 0175 53 93-5 



F. cantiana ... 176 12 15 0*24 89 214 



Ch. lapicida ... i7"6 7"6 0*19 70 134 



X. pisana ... 17*3 13*4 023 ioi 232 



A', virgata ... I3'i 99 0*22 59 130 



A', ericetorum ... i8 - o 97 0*13 134 175 



X. caperata ... g - i 5"6 C13 39 51 



F. carthusiana... 117 70 0-12 68 82 



Besides showing that larger shells are proportionately 

 thinner than smaller ones, it will be seen that the first 

 five species are, on the whole, thinner than the last five 

 / dlam. x alt. r \ ,, . ^ 



I . . , ■ 967, as against 802). Moquin-Tandon 



(" Histoire," i., p. 292: 1855) quotes a species preeminently 

 not belonging to this group as the thinnest (Fruticicola fnsca), 

 and one pre-eminently belonging to the group as the thickest 

 (Leucochvoa candidissima). Mr. Bowell tells me that some 

 Leucochvoa which he has examined do not run beyond 

 o'5 mm. thick These two species are especially instructive, 

 as while Leucochvoa is not a Helicella (—Xerophila), Fruticicola 

 fusca is not far removed from that group ; their physiological 

 does not correspond with their morphological anatomy, but 

 is just reversed, and such questions as the present belong to 

 physiology. 



I am indebted to Mr. Bowell for the following brief sum- 

 mary of the morphological relationships ofourEnglish Helices. 

 " The genera Punctual, Morse (P. pygntaeum, Dr.) and Pyrami- 

 dul.i, Fitz. (/ J . rupcstris. Dr., and P. rotundata, Mull.) belong, as 

 Pilsbry has most conclusively shown, to the Endodontidae, 

 and are quite distinct from our other Helices. To quote: 

 " This family is intermediate between Zonitidae and 

 Helicidae in its cbaracters, and it is decidedly less special- 

 ized than either. While it may not be in the direct line of 

 descent of these two families, it is certainly nearer than 

 either of the others to the common ancestor of the three, as 

 is shown by its unspecialized jaw, teeth, genitalia and shell. 

 Palaeontology has yet given but little to the history of the 

 group, but that little is significant; the Carboniferous of 

 Nova Scotia has afforded a small Helicoid described as 

 Zonites priscus, Cpr., which in form and ribbed-striate 

 sculpture can only be compared to such Endodontidae as 

 Pyramidula or Charopa." (" Guide to Helices," Introd., 

 p. xxxix.) If we also eliminate for separate consideration 

 the genera A canthinula and Vallonia, which in all probability 

 belong to an older fauna, the remainder ot our '■ Helices " fall 

 naturally into three groups: {a) The most highly developed 

 Helicidae are represented here by the forms asptrsa, pomatia. 

 nemoralis and hortensis. Pilsbry has, I think rightly, reduced 

 the names Cryptomphnlus. Helicogena and Tachea to the level 

 of "sections," retaining the old generic name " Helix" for 

 the species formerly known under these names (together with 



that in large, arid desert areas, — the Sahara, to 

 take an extreme instance, — though the temperature 

 may rise very high during the day, at night it goes 

 to the other extreme, and animals have to make 

 themselves secure against the attacks of frost. 

 This pale mode of coloration is the one character- 

 istic of desert species, as seen in Helix desertorum ( 5 ) 

 or H. lactea. That they flourish in such situations 

 is shown by the fact that specimens from the 

 Algerian Sahara are actually larger than the 

 ordinary European form of the same species. 



It has been made out that widely distributed 

 species, such as Helix pomatia, Xerophila- pisana, or 

 Leucochvoa candidissima, from desert localities, are 

 thicker than the type, and tend to lose all trace of 

 coloured bands ( c ). Just as we find these modifica- 

 tions strongly accentuated in localities which are 



a number of allied species, of course). Helix pisana. Mull., 

 though apparently a very degenerate or much modified form, 

 seems best placed here. (Pilsbry gives Euparypha as a sub- 

 genus to mark its aberration.) (£) Helicigona, Fer., is a very, 

 distinct genus, quite unlike He Ux (" Guide," p. 297), as indeed 

 anyone may convince himself by dissecting either of our two- 

 native species {lapicida and avbustorum) and looking at the 

 large simple mucus ("digitate") glands. The form of the- 

 spiculum is also characteristic, and that of the diverticulum 

 (enormously large) betrays Helicigona at once. The only- 

 other European species are quinipcnana,F6r. (= kertnorvam, 

 Moq.) ; the species of the raspailii group (all from Corsica 

 and Sardinia) ; the Alpine species of Chilostoma, and certain. 

 forms like H. aethiops. Biz., which are closely related to 

 arbustorum. The variation in form and colour in this genus, 

 may be compared with that obtaining in Helix and in our 

 third group; nearlv everything may be parallelled— conoidity,. 

 globosity, planorbiformity ; brilliancy of decoration, or quiet 

 colouring. But we do not find the extreme of brilliancy nor- 

 that form of shell which Mr. Boycott, rightly I think, regards 

 as most perfect, to the same extent as in Helix; and a still 

 less specialized series is found in (Y) the genera HelUcella- 

 and Hygromia. With the latter we may class Helicodonta 

 obvoluta, Mull., which, though aberrant, is clearly connected 

 with it. Hygromia is the earlier genus of the two, and com- 

 prises our species fusca, Mont., granulata, Aid., hispuia, L., 

 revelata, Fer., and rufescens, Penn. (according to Pilsbry, 

 though I think the latter should belong to the Theba group). 

 In ru/cscens we see the beginnings of real colour variation, 

 and that part of the genus Helicella known under the sub- 

 generic name Thcba (our species cantiana, Mont., and 

 carthusiana, Mull.) naturally follow the lead of rufescens and! 

 exemplify in all probability the mode of origin of banding in 

 the Helicidae. Theba is a section oi Helicella, which contains- 

 our remaining Helices, viz., variabilis, Dr., virgata, Da C.,. 

 ericetorum. Mull., caperata, Mont., and the aberrant form. 

 acuta, Miill. This classification was based upon anatomical, 

 considerations, but it will be seen that it greatly assists the 

 study of the shell. For example, in the Hygvomia-Helicella- 

 section we meet with much greater diversity than in the other 

 two : anatomically we find the flagellum short, except in one- 

 species {Helix fusca, Mont.) ; some species have two spicula^ 

 others one, and others again {carthusiana (?) acuta, revelata) 

 none. In the relative size of parts there is the greatest 

 variation even between apparently closely allied species ; in 

 the shells nearly all the further developments of the true 

 Helix are hinted at. Many of the species seem to retain the 

 migratory habits which doubtless characterized the ances- 

 tors of the Helicidae, and the gregarious character of all may 

 probably be another sign of " ancient lineage."— E. W. W. B. 



(-i I am not inclined to include Fruticicola cantiana (a 

 Helicella) in the erouo ; its habits and habitats are much 

 more like those of Tachea than Xerophila. 



( 3 ) For this in Fruticicola carthusUna, see L. E. Adams, 

 J ourn. of Conch., viii. (1896), p. 319. 



( 4 ) Readers need not be reminded that the temperature of 

 Mollusca is always slightly above that of the surrounding 

 air, at least within the ordinary range of variation. 



(») This also may well be cryptic on sand. 



(6) A. H. Cooke, Cambridge Nat. Hist., iii„ pp. 25, 85.. 

 (1895). £/■ also J. \V. Taylor, Journ. of Conch., v., p. 297. 



