COCKERELL AND COLLINGE : CHECK-LIST OF SLUGS. 227 



same as Neojanella, but if Messrs. Hedley and Suter can 

 affirm that individuals agreeing with bitentaculata (ant/fio- 

 daruiii) do grow to a length of 53 mm. (as measured in 

 alcohol), and that when so grown they agree with my 

 description of Neojanella dub/a, of course I have nothing 

 further to say. I very much hope that conclusive proof 

 will soon be offered, one way or the other. 



Hyalimaci/icc. Mr. Hedley refers to the anatomy of 

 " Parma' ion''' kersteni, V. Mts., which appears to make it 

 a member of this group. Its proper generic position is still 

 undecided, and my information about it does not enable 

 me to offer any opinion. 



Another "Parmarion" which I do not understand is 

 rang/anus, Fer., from Bourbon and (it is said) Madagascar. 

 Tryon gives it as a Parmarion, and Gray (B. M. Cat., 1855) 

 cites it as a doubtful Drusia. It has also been called 

 Parmacella rang//. I had an idea it was a Hyalimax, but 

 Mr. Hedley makes no mention of it in his " Enumeration," 

 and I have not now access to the literature that might 

 enable me to decide about it. 



CONCLUSION. 



In concluding the list, I wish to point out that it is necessarily 

 •very far from perfect, and that the progress of knowledge concerning 

 slugs must inevitably require great changes to be made, even in 

 respect to matters which now seem beyond dispute. The compiler 

 of such a list knows its weak points better than most of its critics 

 •can know them — knows how often it has been impossible to decide 

 with any certainty about the validity of a species ; and how often 

 one opinion has seemed about as good as another, and has been 

 followed because some choice had to be made, rather than because 

 it was probably correct. 



Probably there are few things so prejudicial to the progress of 

 science as the spirit of confident assertion which will not readily 

 admit the possibility of error, or consider the views of one who 

 thinks differently. To illustrate the dangers of such an attitude, 

 I may instance the radical changes which have taken place of late 

 years in our views respecting the species of Ar/on. Kobelt's catalogue 

 (1881) may undoubtedly be taken as compiled from the best sources, 

 and to represent the opinion of the time, yet when we turn to Arion 

 in the index, we find as follows : — 



