268 ASHFORD : ON THE DARTS OF BRITISH HELICID^. 



estimated from Moquin-Tandon's anatomical details (not always 

 fully given) lies between 60 and 66. According to Dr. Leidy, 

 the United States are remarkably deficient in indigenous dart- 

 bearing species. Only four such were known when A. Binney's 

 work appeared in 1851, and these four are now considered 

 referable to Zonites rather than Helix. Since that date, anato- 

 mical investigation has been greatly extended, and the number 

 just quoted has certainly been increased, (cf. ' Notes ' by W. G. 

 Binney, 1856 — 1875...) but I have no summary at hand from 

 which to estimate a per-centage. Of the structure of tropical 

 Helices, but little is known beyond the shell. 



Here these notes might with propriety close. But it is 

 thought the subject will be rendered more complete if brief 

 reference be made to a few other British species which, though 

 not furnished with darts, are more or less allied in structure to 

 those possessing them. They are as follows ; — 



Helix revelata Mich., pi. x., fig. i. This has a rudimentary,* 

 naturally empty, sac on each side of the broadly dilated 

 vagina, obscurely bilobed in adults and surmounted by four 

 short but perfectly characteristic, opaque, whitish or 

 yellowish mucous glands, two on each side. In immature 

 examples the sacs are scarcely perceptible and the mucous 

 glands shorter. The figure is drawn from one of a parcel 

 kindly sent me by Mr. B. Tomlin, of Pembroke College, 

 Cambridge, and collected by him in Guernsey in the month 

 of July. 



Helix obvoluta MiilL, pi. x., fig. 2. Has a long ceecum 

 attached to the vagina close below its junction with the 

 spermatheca-duct, and having at its inferior extremity 

 another but much shorter coecum. Moquin-Tandon 

 considers these to constitute a mucous gland with a branch. 

 Schmidt, on the contrary, thinks the longer tube may be 



* I may be technically wrong in calling these sacs rudimentary ; perhaps 

 the are nascent. 



J.C, iv., Jan., 1885. 



