ASHFORD : ON THE DARTS OF BRITISH HELICID^. 79 



Systematic Value. That an organ confined principally to 

 a single genus can have little weight in the arrangement of higher 

 groups is self-evident. On the other hand, it can scarcely be 

 denied that the type of dart, in virtue of its remarkable constancy 

 in the individuals of a species, is a valuable criterion in the 

 discrimination of closely allied forms, and in very critical cases 

 may be allowed, so to say, a casting-vote. What relative weight 

 should be assigned to dart, shell, jaw, lingual-ribbon, etc., in 

 the subdivision of the unwieldy genus Helix into large groups, 

 must be left to the judicious systematist. 



Miscellaneous remarks. Schmidt considershehas detected 

 a relation between the form of the dart and the colour, number 

 and disposition of the bands of the shell. Morch, summarising 

 that author's observations, says that species furnished with a 

 pyramidal subulate dart, associated with mucous glands having 

 more than eight coeca, have (normally) never more than five 

 bands ; that those with a dart of the type of that oiH. arhiistorum , 

 and two simple or bifid mucous glands, have never more than 

 four bands; and that two subulate curved darts are associated 

 with shells having numerous linear markings. It is highly 

 probable that some such relation exists among forms belonging 

 to the same stemma, but until something is ascertained of the 

 anatomy of thousands of tropical forms, as yet only known by 

 their shells, it is premature to lay much stress upon such rules. 

 Advantage will however arise from calling attention to the 

 subject. Paasch is of opinion that the dart occurs only among 

 those species whose egg-envelopes are lined with calcareous 

 crystals. Schmidt has found in the reproductive organs of 

 Bulimus a cuius, and one or two of its allies, an unguiform, 

 calcareous plate, which Morch thinks may perhaps be the 

 analogue of the Helicine weapon. 



The dart may in a few cases be satisfactorily extracted for 

 preservation by careful dissection, but it is generally safer and 

 often indispensable to boil the sac in a solution of caustic 

 potash. Goldfuss recommends this process in all instances, 

 o*o»o 



