ON A NEW HISTRIOBDELLTD. 299 



On a New Histriobdellid. 



By 



Willinm A. Ilaswell, M.A., D.Sc, F.R.S., 



Challis Professor of Biology, University of Sydney. 



With Plates 14 and 15. 



Introduction. 



During a recent visit to Tasmania I found the minute 

 animals Avhicli form the subject of the present paper living 

 in abundance in the branchial chambers of the fresh-water 

 crayfish (Astacopsis tasm aniens) that occurs in streams 

 in the neighbourhood of Hobart. I am greatly indebted to 

 Mr. Alexander Morton, F.L.S.^the Curator of the Tasmanian 

 Museum, for his kindness in facilitating my work in Hobart 

 by every means in his power, and also for afterwards pro- 

 curing and sending to me in Sydney specimens of Tasmanian 

 crayfishes. 



Histriobdella homari,^ the only known relative of the 

 new animal, is found living among the eggs of the European 

 lobster (Homarus vulgaris). The first recognisable 

 account of it was given by P. J. van Beneden (2) in 1858. 

 Our knowledge of this remarkable animal was greatly 

 extended in 1884 by Alexander Foettinger (6), who supple- 



' Fcettinger's alteration of both the generic and specific names does not 

 appear to be necessary, and van Beneden's name must apparently be re- 

 stored. Histriobdella is certainly not a leech ; but the name Histriodrilus 

 proposed by Foettinger does not indicate its true affinities vrith any greater 

 exactness. Moreover the termination " -bdella " occurs in the accepted 

 names of several genera that do not belong to the Hirudinea, 



