COLLINGE : FURTHER REMARKS ON BURROWING HABITS. 29 



conchoiogist will be found to adopt such an arrangement. The 

 true result, following the researches of Simroth and others, is that 

 the Arionidce constitute a distinct family ; but the validity of the 

 Limacida: as a family group still remains, and it still remains true, as 

 I believe, that the Arionida are more related to the Helicidce than to 

 the Limacida:. Thus the arrangement given by me in P.Z.S., 1891, 

 p. 216, based largely on characters of the jaw and lingual ribbon, is 

 in no wise affected. 



In classifying slugs it is very difficult at times to find good 

 characters to distinguish groups, and probably the jaws and lingual 

 ribbon are, on the whole, as useful as any others, if used with 

 caution. Dr. Scharff relies in part upon the shell and caudal gland ; 

 but it must be remembered that some Arionidce have a calcareous 

 shell, while the caudal gland, although present in Avion, is wanting 

 in Anademis and other genera belonging to the same sub-family, and 

 is present in various tropical genera of Limacida:. How far the 

 other characters hold good, we are not yet altogether in a position 

 to judge, and further researches into the anatomy of the several 

 genera, such as those Dr. Simroth has so ably conducted, are much 

 to be desired. 



Kingstown, Jamaica, 



May 1, 18Q2. 



SOME FURTHER REMARKS ON THE BURROWING 

 HABITS OF CERTAIN LAND MOLLUSCS. 



By WALTER E. COLLINGE, 



Assistant Demonstrator in Zoology, St. Andrews' University. 



My observations " On the Burrowing Habits of Certain Land and 

 Freshwater Molluscs " * seems to have awakened some little interest 

 in the subject, and has induced me to give further and closer 

 attention to a matter of such importance. 



In speaking of Geoma/aa/s maculosus, Allm., I quoted the well- 

 known observations of Allman and Jeffreys on this species, but 

 purposely refrained from commenting upon the same until they 

 were verified by some other observer, as I doubted both statements. 

 Dr. Scharff, who has not only paid careful attention to this species 

 in captivity, but also in its natural habitat, writes me: "I quite 



* "Naturalist,'' p. 75 (1891). 



