305 
have applied this name to forms of the Littorina obtusata group, 
whereas Mårch (10) and Westerlund (15) have used it to denote a 
brackish water variety of Neritina fluviatilis, Linné. There can be 
no doubt that the first named authors have misapplied the name. 
Linné in his Fauna Suecica (2) writes of Nerita littoralis: ,,Ani- 
mal utrinque setas duas instar pedum totidem exserens.” There is 
nothing in the L. obtusata group, however, to which this cha- 
racter can be referred. Moreover he writes ,,Habitat in Lacu ad 
pagum Tible Uplandiæ frequens,”-- but no Littorina lives in the 
Swedish lakes. The fact, that neither in his Fauna Suecica nor 
in his Systema Naturæ does Linné describe WNerita 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 Littorina 
are closely allied, and it has sometimes been suggested thay they 
produce hybrids. H.E.Sauvage (19) has observed Littorina litto- 
rea in copulation with Littorina rudis, but no progeny is known. 
Copulation has also been observed between L. rudis 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, Littorina littorea, 
L. rudis and L. obtusata. Friele (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 much stress on the radulæ which undoubtedly are abnormal 
I can not but incline to his opinion that in Buccinum — as in 
Littorina — 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, 
