ESMARX: MOLLTJSCA OF NORWAY. 121 



Subgenus SEGMENTINA Flem. 

 P. nit id US Miill. Rare. Bergen. 



Subfam ANCYLINA. 



Genus ANCYLUS GeofF. 



Subgenus ANCYLUS Geoff. 



Ancylus fluviatilis Miill. Not common. In the vicinity of 



Christiania, Sandefjord, and Jaedderen. 

 A. fluviatilis var. gibbosum Bourgt. More common than 

 the preceding species. Christiania, Asker, Sognselven, 

 Fiskmn^ and Skien. 



Subgenus ACROLOXUS. Beck. 

 A. lacustris L. Christiania, Brevik, Skien, Arendal, and 

 Jsedderen. 



Genus PISIDIUM C. Pfr. 

 Subgenus RIYULINA Cless. 



Pisidium globulare Cless. Rather common. Many places 

 near Christiania, Ringsaker at Hedemarken, Romerige, 

 Ringebu, Tdnset, in Hamar Stift ; Langevand, near 

 Bergen ; also in Christiansand Stift ; Maalselven, in the 

 Amt of Tromso ; Porsangerfjord and South- Varanger in 

 Amt of Finmarken. 



Subgenus FOSSARINA Cless, 



P. henslowianum Sheppard. Bergen. 



P. fossarinium Cless. Very common. Many places round 

 Christiania, Drobok, Laurvik, Porsgrund, Romerige, 

 Hvaloerne, ' Siljordvand' in Telemarken, Tonset in almost 

 all lakes, and as far north as Maalselven, Tromsoen, Pors- 

 angerfjord, and South- Varanger. 



P. fossarinum var. flavescens Cless. Krodsherred, Chris- 

 tiania Stift ; Trondenses, in the Amt of Tromso ; Alten, in 

 the Amt of Finmarken. 



Abnormity. — ' Colour white, glossy ; lower margin is not 

 straight, but impressed from the side ; from the underside 

 it looks like fig. i, from the side it is long and narrow, as 

 in fig. 2, Something like this form lias also been seen in 

 Unio. It is sure to be caused by external circumstances.' 

 (Clessin in letter.) 



