SCIENCE-GOSSIP. 



i95 



- tail to penetrate small holes, and, in the case 

 1, the most familiar instance, to follow 

 is down their holes, and so secure food. 

 The shell may become partially covered by the 

 reflexion of the mantle ( Vitritia, Physa, A mphipeplea), 

 which leads to total inclusion (Linux), and con- 

 sequent atrophy (Arion). This loss of the shell is 

 generally followed by a compensatory adaptation 

 for protection, such as great capacity for regenera- 

 tion, and colouring which may be protective in 

 various ways ( l ). It is to be remembered that the 

 bilateral symmetry also arising is only external, 

 never internal. 



The patelliform shell, exhibited in the fauna 

 we are considering by Ancylus, is very widely 

 distributed throughout the mollusca, in various 

 groups, both recent and fossil, e.g.. Patella (also 

 under this name from Oolite), Ancylus, Piieolus 

 lOoIite . C 1 I Silurian), etc. This shell form 



is an advanced modification : Ancylus and Patella 

 have an embryonal spiral shell, and the flattened 

 cone is a new acquisition, modified for a sedentary 

 life amid quick currents. Ancylus fluviaiilis lives in 

 security on stones exposed to streams of very 

 considerable violence. Neritina is similarly modi- 

 fied, as far as its external shape goes, and enjoys 

 the same advantages in similar situations ; Navicclla 

 is much the same ('-). 



Turning now to the coloration, we may com- 

 mence by studying the coloration of the shell in 

 those forms which bear it externally (■'■). Roughly 

 speaking, by their coloration, the British terrestrial 

 species (which may conveniently, though not in 

 many cases very properly from a morphological 

 point of view, be examined apart from the aquatic 

 forms) may be divided into two main groups, with 

 further sub-divisions, as follows : 



■ tic. The prevailing tint may be : 

 Brown and 'horn-coloured" of various 

 shades. Ilyalinia (except f*)pura), Conulus, 

 Patula ruftstris (?), Punctum, Acanthinula 

 I "- lamtllata), Trigonostoma, Fruticicola ru/eseens, 

 F . hi ran Ua, F. revelata (greenish), 



F fusca, Buliminus, Pupa, Vertigo, Balca 

 (sometimes with a faint greenish tinge), 

 irk, metimes slightly 

 variegated with white), Azeca, Cochlicupa, 

 Sucanea, Acicula. Some of these are varie- 

 gate: irci perUti mes {e.g., red in 

 Cochlicupa. white in Claustlia, occasionally a 



1 !.-.n«. Cornp. Ana- Trann.), 



. 4JO. 



"II In »Iuk". i ntvei 



W(!h ifafl B0 -■' Ol •'■• I' ' Of ':.»■ ;.,.li,.,t iri .,: ; . | . ,4! -..,■/. 



■ 'I'tlae in 



pleat." 



red rib in, e.g., F. hispida), but this is very 

 largely invisible externally. Some Hyalinia 

 have their underside of a clear, bright white. 



(/3) White : Hyalinia pura. Discus (Vitrea), Val- 

 lonia, Fruticicola cantiana (generally with a 

 strong reddish tinge), F. carthusiana, Caeci- 

 lioides, Carycliium, and white varieties. 



(7) Green: Vitrina; slightly, Fruticicola 'revelata. 

 (2) Oligochromatic. 



(a) Of dull, lugubrious colours, mostly browns: 

 Patula rotundata, Chilotrema. 



(/3) Of brighter, often paler, colours : Helix 

 (pomatia), Cryptomphalus, Atlanta, Cyclostoma. 



(7) Of a general coloration of black and 

 white : Xerophila, Cochlicella. 



(8) Of comparatively bright colours : Tachea. 

 Of course, these groups run into and overlap 



each other. For instance, Cryptomphalus may be 

 practically monochromatic (black or yellow) on 

 the one hand, while at the other end we find 

 specimens (var. tigris) which rival Tachea in the 

 brilliancy of their tints. 



According to the general rule, that in animals of 

 very small size significant coloration does not 

 exist ('), or at any rate is not recognizable, we may 

 leave such genera as Carycliium and Vertigo out of 

 consideration. According to another general rule, 

 viz., that bright varied colours are not developed 

 except in those species which live fairly freely 

 exposed to light and warmth, we should naturally 

 expect the group with dull, monochromatic shells 

 to live in dark, damp situations. This is actually 

 the case : they live under stones, under bark on 

 trees, among dead and rotten leaves, and in similar 

 places, from which they only emerge on damp days, 

 when the sun is obscured, or during the night. 

 This explanation will not, however, suffice for all 

 the species included in the first group: Fruticicola, 

 cantiana lives very much in the open, and is really 

 comparatively brightly coloured ; F. carthusiana 

 leads a still more exposed life, and will be dealt 

 with later. Succinea lives in the open in great 

 measure, and its shell may possibly be explained 

 in the same way as Limnaea, it being always a 

 possibility that it is derived from the aquatic 

 Pulmonata (see below). Fruticicola rufescens, e.g., 

 really moves about just as much in the open as 

 Cryptomphalus, and very nearly as much as Tachea. 

 After rain in the daytime, it and Tachea are often 

 found swarming together on nettles, crawling 

 about quite freely, when Fruticicola hispida, etc., 

 have not yet emerged. It has a rather thicker 

 shell !h;in the other members oi the group. 



The next group we may take up is a very 



well defined one on the whole. It contains 



1 Xerophila and Cochlicella, to which may 



I:, i., mi, : ,,1 tnd 1 -V otbi i i mall i"i mi have 



mb i' nopi ii' 'l ihoott on twigs of 



■ to,"— E. sv. w. Bowi 11. 



» 3 



