299 
Littorina tenebrosa 
1) The central tooth has 3 denticles. 
2) The first lateral tooth has 3 denticles. 
3) The third lateral tooth has i denticles 
With regard to the central tooth it is true that 5 denticles 
are sometimes to be found on that of the so called L. groenlandica. 
Teilman-Friis records this number in Norwegian specimens. In Sars's 
figure of L. groenlandica from Norway, however, the central tooth has 
only three denticles (20), and I have noticed the same number in 2 spe- 
cimens from Greenland, 3 from Iceland ") and 4 from Norway (Fig. 4). 
Møbius has in some cases noticed more than 3 denticles in L. rudis 
var. tenebrosa. He writes concerning it as follows (18, Pag. 18): 
»Die Krone hat einen breiten und langen Mittelzacken, an jeder 
Seite desselben steht gewdhnlich ein kleinerer Zacken, an welchen 
sich noch ein oder mehrere Spitzchen anschliessen”". 
On the first lateral plate I have noticed in three speci- 
mens ' four denticleg in L. tenebrosa, four ålso im two cases of 
SES 
a,b VR E REED, RÅ snilde from Smaalandsbugten, mang ec The adel tenebrosa 
m Bordeyri. Iceland. d The Littorina groenlandica from Greenland. 
e The Littorina groenlandica from Berufjordr, Iceland. 
L. groenlandica from Greenland, and 5 in three cases of L. groen- 
landica from Iceland. (Fig. 5). Compared with Teilman-Friis's re- 
1) The common forms of L. rudis from Iceland were considered by Mørch 
to be L. groenlandica, Menke (7). 
