354 Mr. N. Colgan on Locomotion and the 



32. Pelomysfallax, Peters. 



? . 15. Kambove. 

 (^.80; $.73,82. Bunkeya River. 

 " Native name ' Liwendi.' Resembles Dasymijs hentleyce 

 in its habits." 



33. Georychus mellandi, Thos. 



(J . 40. Lualaba River. 



(J . 42. Upper Lualaba River. 



" Native name ' Mi'uko ' or ' Malevi.' " 



34. Georychus amatus, Wrought. 



(J. 21, 22, 26; ? . 24, 25. Katanga. 

 " Also called ' Mfuko.' " 



XLVI. — Notes on Locomotion and the Use of Slime-threads in 

 the Marine Mollusca. By Nathaniel Colgan, M.R.I. A. 



While engaged last year in studying the Nudibranch fauna 

 of County Dublin the writer of these notes was induced to 

 make some observations on the locomotive powers of certain 

 species of marine Mollusca chiefly belonging to the Gastro- 

 poda, and as the results arrived at appear to be in some 

 respects sufficiently novel to merit permanent record, they are 

 set out here in some detail. In all 18 species were dealt with, 

 10 Prosobrancbs, 7 Opisthobranchs, and 1 Filibranch, and 

 the aim of the inquiry was not so much to determine the rate 

 of travel of the various species as to ascertain whether any of 

 them were accustomed to make use of suspensory slime-threads 

 as an aid in locomotion. 



Every student of the marine Mollusca is familiar with the 

 fact that the Gastropods in general have a strong propensity 

 to float foot upwards on any still-water surface they may be 

 enabled to reach by crawling, and that many of them are 

 accustomed to suspend themselves beneath that surface by 

 means of slime-threads or attenuated strings of the mucus 

 which all of them so freely secrete. But hitherto observation 

 does not appear to have very conclusively established the fact 

 that the power of re-ascending by such threads to the water 

 surface is possessed by many of our native species of marine 

 Mollusca. H. WalHs Kew, indeed, in his well-known paper 

 on Spinning Molluscs in the * Zoologist ' for July 1900, states 



