242 ASHFORD : ON THE DARTS OF BRITISH HELICIDiE. 



Rather high up are eight mucous glands, or perhaps they 

 should be described as four in number disposed in very deeply 

 divided pairs. They are about 3 mm. long, usually simple, 

 occasionally bifid, rarely trifid, stout and stiff with opaque white 

 or buff cores and supported by short, thin, flexible stalks. Here 

 and there may be noticed a curious stricture as if the branch 

 were tied round tightly with dark brown thread. Though eight 

 is the usual number, seven or nine sometimes occur. 



An instance of misgrowth has come under my notice where 

 one dart-bearing sac was properly developed, the other arrested 

 at an early stage. A similar case has already been referred to 

 in H. ericetorum. 



The twin darts are generally alike but vary in different 

 individuals. Sometimes they are perfectly straight like little 

 circular obelisks, sometimes curved and awl-shaped. There is 

 no appearance of even rudimentary blades. The basal expan- 

 sion is relatively very large and often asymmetrical with a more 

 or less wrinkled surface and attenuated margin. Figs. 10 and 

 1 1 shew the extreme limits of variation among the specimens 

 in my collection. A very common form is intermediate, the 

 shaft but slightly curved and the base apparently set on askew. 



I have never found both darts absent from a mature shell, 

 and very rarely even one of the couple. They appear to be 

 retained throughout the winter for they have occurred as 

 uniformly, when sought for, in December, January, and Febru- 

 ary as in the other months. Perhaps the comparatively large 

 base affording, as it must, a greater area of attachment to the 

 tubercle may partly explain why the weapons are so seldom 

 lost. A noteworthy feature is the position of the dart-sacs which 

 are removed by nearly three times their own length from the 

 external aperture. Are both darts brought into action at once ? 

 No one appears to have recorded any observations of the 

 gladiatorial encounters of the smaller species. 



An animal dissected in the last week of July was found to 

 have been killed while depositing or about to deposit its eggs. 



J.C, iv., Oct., 1884. 



