132 



SCIENCE-GOSSIP. 



COLOURATION AND ZONULATION IN TACHEA. 

 By A. E. Boycott. (*) 



TpVERYONE is familiar with the brightly- 

 J — ' coloured snails — red, yellow, brown, some 

 marked with bands, some plain — which abound in 

 almost every hedge-bank in rainy weather. They 

 are known as Tachea memoralis, L., and T. hortensis, 

 Mull., and form the genus Tachea of the great 

 group Helix. I propose to call attention to a few 

 points connected with the variation in colouring 

 and banding to which these snails are subject in 

 Herefordshire, dealing with them as grouped into 

 different batches by differences in either the time 

 or the place of their origin. There is one case of 

 especial interest which, by the kindness of Mr. A. 

 C. de Boinville, of Plymouth, I am enabled to deal 

 with. This gentleman collected numerous speci- 

 mens of Tachea in the immediate neighbourhood 

 of Hereford some fifty years ago (mostly in 1S43), 

 and it seems worth while to see how far this 

 collection which — amounting to some 730 speci- 

 mens — he has been good enough to place in my 

 hands corresponds with and differs from the same 

 species found around Hereford at the present day. 

 There is further to be considered how far these 

 species differ in various localities, separated by 

 short or long distances, especially considering 

 differences in geological formation. At present 

 I only bring before you a comparison of the 

 specimens from the large quarries of Wenlock 

 limestone in Dormington Wood, near Stoke Edith, 

 with those from various stations in the Old Red 

 Sandstone. 



It is obvious that to obtain exact results, every 

 specimen (personally, I confine myself to full- 

 grown specimens, judged by the peristome) to 

 be found in the locality under examination must 

 be collected and considered. Every shell of one of 

 these catches is carefully examined as to its colour, 

 banding, size and shape, weight, thickness, and 

 any other. peculiarities. I have thus worked over 

 about 2,500 Herefordshire Tachea, but hope to do 

 many more in the future ; the more numerous the 

 examples, the more nearly will our conclusions, 

 percentages and averages approximate to the truth. 

 There is no doubt that this condition, which I 

 have prescribed for my own collecting, has not 

 been rigorously adhered to in the case of the 

 De Boinville collections, but from what Mr. de 

 Boinville has told me as to his methods, I do not 

 think that the figures are so far from representing 

 the truth as might be suspected. At the same time, 

 I claim for them none of the accuracy which I 

 think is to be found in the other cases I am bring- 



(')Read before the Woolhope Naturalists' Field Club, at 

 the meeting held August 27th, 1S97, at Bewdley. 



ing before you ; and it is plain that collections 

 consisting of the striking specimens only are useless 

 for the purpose under consideration. 



The localities I consider to day are five in 

 number : (1) Dormington Quarries (SS specimens), 

 in District 3, on the Silurian limestone ; December, 

 1893, and January, 1S94. (2) De Boinville collec- 

 tion (737), from Districts 7 N and 7 S, on the Old 

 Red Sandstone ; circa 1S43. (3) Moreton-on- 

 Lugg (540), District 7 N, on the Old Red Sand- 

 stone; July, 1S96. (4) The railway bank, near 

 Hunderton (216), District 7 S, on the Old Red 

 Sandstone ; April, 1S95. (5) Broomy Hill, near 

 Hereford (308), District 7 N, on the Old Red 

 Sandstone; April, 1895. 



Firstly, as to the proportion between these 

 species. The superficial distinction in the colour 

 of the peristome (black or brown in T. nemoralis, 

 white or nearly so in T. hortensis) seems to hold 

 good, or at any rate to be verified, in the cases 

 which I have examined by the speculum in 

 Herefordshire. I have not seen a local nemoralis 

 with a white lip, and the form bimarginata, Picard, 

 is uncommon. Of all the 1S89 specimens here 

 considered, 55 per cent, are nemoralis and 45 per 

 cent, hortensis. Dormington Quarries have a re- 

 markably low percentage (9) of hortensis. For 

 further details see the appended Table I. 



Secondly, to consider the variation in colour. 

 In T. nemoralis there are four main colour types in 

 Herefordshire, as distinguished in the main by 

 their ground colour. These are : 



(a) var. castanea, Moq., of a brown of varying 

 depth ; the best marked specimens are of a very 

 fine rich 'dark brown, with a blue-purple shade 

 inside and a well-marked yellow rim adjoining the 

 peristome externally. 



(b) var. libellula, Risso., of a yellow colour. 



(c) var. rubella, Moq., of a red colour. 



(d) var. " mista." I have ventured to apply this 

 name, for my own use, to a form which is very 

 common in Herefordshire. It is typically heavily 

 banded with dark bands, and the ground-colour is 

 of no very bright or definite colour. It is really — 

 as has been done in some of the late tables — to be 

 classified under rubella. There is no doubt that as 

 the bands increase in number and depth of colour 

 the red ground-colour decreases in intensity. The 

 interesting theoretical conclusion derived from this 

 and similar facts, viz., that the bands are areas of 

 concentrated ground-colour, need not here be 

 further pressed. The term rubella by this division 

 becomes practically restricted to specimens (1) with 

 light, often reddish bands ; and (2) to those with 



