ii8 



NOTES ON THE SECTION TACHEA OF HELIX. 



By EDWARD COLLIER. 



(Read before the Society, JNIaich 12th, 1913). 



The Genus Helix contains the most highly organized species of the 

 Family Helicidce, and the members of the Section Tachea seem to be 

 amongst the most highly specialized forms of this genus, and evi- 

 dently fitted for meeting widely diverse conditions of existence. 



This section is held by some to have originated on the Central 

 Asian Plateau, by Dr. Scharff and others in South-western Europe, 

 but Mr. J. W. Taylor maintains "that its true evolutionary area is 

 decidedly within the Germanic region, from whence it has spread 

 and is gradually spreading in all directions, penetrating eastvvardly 

 through the South Russian provinces by precisely the same route as 

 Helix po/Jialia, thus contributing to confirm this as the true east- 

 ward track of the dominant European species." 



Tachea is one of the most dominant European groups, and is found 

 nearly all over Europe, except in the eastern portion of Russia. One 

 species has extended its range from Spain into Morocco, another 

 species is found in Asia Minor, while one — and that the largest of 

 the group — is found in the Caucasus, and on into Persia, along the 

 southern shore of the Caspian Sea. Another species, and that one 

 of the commonest, has extended its range into North America. 



The Tacheas are of very ancient lineage, as H. nemoralis is recorded 

 from tlie Lower Miocene deposits in the south of France, and has 

 been found in this country in the Pleistocene and Holocene deposits 

 from a large number of localities. 



The shell is globose to subglobose, or depressed, generally thin, 

 rather solid, smooth in most species, but in the larger species striate, 

 or even malleate. They have an umbilicus open when young, but 

 becoming closed in adult life. Whorls 5, the last deflexed in front, 

 tumid. Aperture wide-lunar, oblique, lip expanded and tliickened 

 within, the columellar margin straight, widened by a blade-like callus 

 within. They are nominally all five-banded, but they are very often 

 found with fewer bands, and in many cases without bands at all. 

 They are the most highly coloured of European land shells, as well 

 as the most variable in colour. They live on shady banks, walls and 

 bushes, in gardens, vineyards, etc., and, while avoiding the direct 

 rays of the sun, are light-loving creatures. 



They are very prolific, and adapt themselves to circumstances of 

 climate and environment in a remarkable way. In this country they 

 are found, since the ground was cultivated and enclosed, on hedge- 



