no ASHFORD : ON THE DARTS OF BRITISH HELICID^. 



a dart. Z. excavatus now keeps it company. The two species 

 present a strong family likeness in their internal organisation. The 

 duct of the spermatheca is as long as the oviduct, contrasting 

 with the short, thickened peduncle of Z. cellaruis, Z. nitidulus, 

 and Z. alliarius. In both the oviduct is of a bluish grey or 

 slate colour. The inferior half of the penis-sheath is dilated 

 and there is no flagellum. The pendent extremity of the dart- 

 sac is also common to both. 



The dart-sac of Z excavatus (fig. 5) is unique inform. As 

 was pointed out in the introductory article, a few of our Helices 

 have an accessory lobe attached to the organ, but in all such 

 cases it lies between the teliferous sac and the vagina and is 

 more or less fused to the latter (pi. ii., fig 3). In the present 

 species the secondary lobe is in no way connected with the 

 vaginal tube. It appears to be of later growth, being absent up 

 to a certain stage of immaturity. A slender filament (muscle ?) 

 connects the main pendent lobe with the oviduct, at least in 

 some cases. A retractor muscle to the dart-sac does not occur 

 among the British Helices, and, according to Schmidt, is un- 

 known in any Helix of the Eastern hemisphere. In this respect 

 the two Zonites under consideration show more affinity with 

 American forms. 



There are no mucous glands, but an oval mass of a green- 

 ish-yellow colour, similar to that described under Z. nitidus, 

 occupies their place. 



The dart (fig. 6) is an exquisitely delicate little weapon, 

 and long for the size of the animal. The head is slightly com- 

 pressed and dilated (fig. 8), the amount of compression varying 

 in individuals according to a greater or less approach to 

 maturity. The degree of twist from the plane of curvature (fig. 

 7) is not always the same. The curve of the shaft is usually an 

 arc of about 60°, but I have met with more than one instance 

 in which there is a sub-angular bend just below the head. The 

 dart springs from a tubercle situated, not at the extremity of 



J.C, iv., Oct., 1S83. 



