244 ASHFORD : ON THE DARTS OF BRITISH HELICID^. 



Mr. B. Hudson, of Middlesbrough. As might be expected the 

 bases were but slightly enlarged (fig. i6). 



The occurrence of empty dart-sacs in mature shells is nearly 

 as uncommon as in the case of ^7. rufescens and even in shells 

 not quite completed the darts may occasionally be found. In 

 September, I received a batch of specimens collected near 

 Wakefield and sent by Mr. G. Roberts, but the shells were not 

 fully matured and did not yield a single dart. 



The figures are from the Stockton examples referred to 

 above, sam[)les of which have been approved by Dr. Jeffreys. 



17. Helix concinna Jeffreys, pi. ix. figs. 18-20. Dart-sacs 



two in number, each bi-lobed and similar to those of 



ff. hispida. Darts two, curved or occasionally straight, 



like the preceding ; annulus absent. Length about 



o"75 mm. 



After a careful examination of many adult specimens of 



this and the last species procured from different parts of the 



country and selected as much as possible from extreme forms 



of each kind, I have failed to detect any constant difference in 



either mucous glands, dart-sacs, or darts. Nor is a difference 



to be expected considering the similarity of the respective 



organs in H. rufescens and H. hispida, between which species 



it is generally agreed H. concijtna takes a systematic place. 



According to Schmidt this conformity of darts obtains also 



among several extra-British members of the European group 



that clusters round JI. hispida. 



As H. concinna of . typical form is rather abundant near 

 Christchurch I have had the opportunity of examining an ex- 

 tensive series. The almost constant presence of darts in adult 

 shells, irrespective of the season of the year, is remarkable, and 

 immature darts occur almost as rarely as empty sacs. 



Fig 18 is from a Christchurch specimen, verified by Mr. 

 J. W. Taylor, fig 19 from a very characteristic shell taken at 

 St. Alban's by Mr. Hopkinson of Watford, and fig. 20 from 

 another Christchurch specimen kindly identified by Dr. Jeffreys. 



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



