130 ASHFORD : ON THE DARTS OF BRITISH HELICIDyE. 



Schmidt remark that the companion darts are not always of 

 equal size and curvature, and I have noticed the same irregu- 

 larity. Some pairs are also much shorter aud stouter than 

 others, even when the animals are of the same size. Equal 

 diversity exists in the amount of twist, which is sometimes con- 

 siderable ; sometimes, especially in immature darts, scarcely 

 perceptible. 



I can find no annulus to the darts of this species. The 

 base, which is not wider than the central part of the shaft, rests 

 immediately upon the tubercle of the sac (fig. 4). Owing to 

 the strong curvature of the weapons, and the fact that their 

 concave lines face each other, the free ends of the darts cross 

 one another when at rest in the sacs (fig. 5). One would have 

 thought that by this arrangement the two points, if protruded 

 far, would diverge too much to permit of both being brought 

 into efficient simultaneous use. 



When freshly extracted from the sacs the shafts are nearly 

 transparent, and the tubular cavity is filled with liquid separa- 

 ted by numerous air-bubbles. These disappear in a few minutes 

 and the darts assume a white opaque appearance. I cannot 

 speak of the form of this dart in its incipient stage of growth, 

 having never met with one less than 2 mm. in length. Above 

 that size all are miniatures of the adult, though their curvature 

 naturally forms an arc of fewer degrees. 



Of fourteen adult shells received from Epsom, in the 

 month of August, thirteen possessed two darts ; the other had 

 one sac empty. Adults brought from Corfe in Dorsetshire, in 

 August, September, and October, were all furnished with a pair 

 of weapons, and all the full-grown examples from Somersetshire, 

 received through Mr. Ponsonby in June, were in similar con- 

 dition. 



Helix ericetorum would therefore seem not to lose its 

 weapon so frequently as some species, or else to repair its loss 

 more quickly. 



The figures are drawn from Epsom specimens. 



J.C, iv., Jan., 1884. 



