323 



32 mm.; f) length 59'5 mm., height 26'5 mm. A few propor- 

 tionally high specimens convey the impression, that they have 

 been unable to develop freely as they are deformed («squeezed»). 



The valves of the East-Greenland specimens are sometimes 

 rather thin, sometimes rather solid; on the whole they cannot 

 be said to be especially thick. At Denmark we find for in- 

 stance a similar variation sometimes leading to still greater 

 thickening of the valves. 



Almost all the East-Greenland specimens have the con- 

 centric lines of increase with intervals very distinct; thus the 

 surface shows a number of deep furrows (a corresponding 

 number of conspicuous ribs may sometimes be noticed on the 

 Inner side); it looks as if the growth is arrested periodically. 

 On a specimen of 84 mm. I have counted 17 — 18 of such 

 concentrical furrows. 



On the East-Greenland coast the hmit of the mussel's 

 distribution may be fixed at about 66° 30' N. It was observed 

 so far north, but not further, by C. Kruuse, when he took 

 part in G.Amdrup' s exploration of the coast. No expedition 

 has found Mytilus edulis in a living state further north in 

 East-Greenland, and the late zoologist Sören Jensen, whom 

 I requested to look for the mussel during the expedition of 

 1900, told me that he had seen nothing of the mussel till he 

 came down to Angmagsalik. 



This makes it still more strange that the Nathorst-Ex- 

 pedition of 1899 should find Mytilus edulis fossil at ca. 73° N., 

 namely at the mouth of Sophia-Sound, 25 meters above the 

 sea-level, and quite inmost in Franz Joseph-Fjord, 10 meters 

 above the sea-level ^). This is, however, not an exceptional 

 phenomenon, the mussel having also become extinct in other 

 high-arctic localities, namely at the icy-sea-coast of Siberia, 

 Franz Joseph-Land, Svenska-Förlandet and Spitzbergen 2). 



^) A. G. Nathorst: Bidrag till nordöstra Grönlands geologi; Geolog. Foren. 



Forhandl. Bd. 23, 1901, p. 304. 

 ^) A more detailed mention of this will be found in Ad. S. Jensen: 



