305 
b«i\e applied this name to forms of the Littovina obtusata gro up, 
whereas Morch (10) and Westerlund (15) have used it to denote a 
brackish water variety of Neritina fluviatilis , Linné. There can be 
no doubt that tiie first named authors have misapplied the name. 
Linné in his Fauna Suecica (2) writes of Nerita Moralis : „Aui- 
mal utrinque setas duas i nstar pedum totidem exserens.“ There is 
nothing in the L. obtusata gro up, however, to which this cha¬ 
racter can be referred. Moreover he writes „Habitat in Lacu ad 
pagum Pible Lplandiæ frequens/* but no Littovina lives in the 
Sw edish lakes. The faet, that neither in his Fauna Suecica nor 
in his Systema Natur æ does Linné describe Ner ita littoralis among 
the Littorinæ, also argues that there is no ground for referring it 
to this species. 
It is evident that the three above mentioned species of Littovina 
aie closely allied, and it has sometimes been suggested thay thev 
produce hybrids. H.E. Sauvage (19) has observed Littovina litto- 
vea in copulation with Littovina vudis, but no progeny is known. 
Copulation has also been observed between L. vudis and L. obtusata 
without progeny being known (W. Thompson, 8, Jeffreys, 14, 
P. Fischer, 16). 
The variation in the radulæ of the Littorinæ, which I have 
examined, is so great that I have not found any constant character 
separating even the three well defined species, Littovina littorea, 
L. vudis and L. obtusata . Frie 1 e (23) and Collin (24) in cer- 
tain species of the genus Buccinum have also found a very great 
variation in the number of denticles. Although Collin appears to 
lay too mueh stress on the radulæ which undoubtedly are abnormal 
I can not but ineline to his opinion that in Buccinum — as in 
L i ttor in a — the number of denticles is unsuitable for determining 
the species. In some cases it may be employed in distinguishing 
the varieties. 
Vidensk. Meddel, fra den naturh. Foren. 1901. 
20 
