336 



The umbonal region is provided with narrow, rather sharp 

 folds which in the fuUgrown specimens are continued shorter 

 or longer down, but without reaching the middle of the shell, 

 and as a rule they keep to the umbonal region. The periostracum 

 is generally thick and bast-like, brown or blackish and fre- 

 quently somewhat shining. 



The East-Greenland specimens are probably to be referred 

 to the ^variety placenta Mörch^). The specimens from Hekla- 

 Havn were examined by Pos seit who set them up as a 

 new variety: sericea on account of the «lengthened shape» of 

 the shell and the «thick epidermis with its silk-like lustre» ^). 

 Only the first mentioned quality might — according to my opinion 

 — though hardly justify the setting up of a special variety and 

 even in this respect numerous transitions to var. placenta 

 exist. 



In a fossil state the species was four^d by the Danish 

 East-Greenland-Expedition of 1900 in the following localities: 

 Hurry-Inlet, INorthern part, Liverpool-Coast 9 valves. 



Hurry-Inlet, Northern part, from different banks, 



Ryders-Elv at the main river 20 — 



They are either fragments or very rubbed valves. 



Nathorst too found it fossil, namely at the mouth of 

 Sophia-Sound at a height of 25 — 40 meters above the sea- 

 leveP). 



^) Mo ich: Catal. des Moll, du Spitzberg; Mém. Soc. Malacol. Belgique, 



T. IV, 1869, p. 22. 



Lèche: Öfveis. öfver de af Sv. exped. til Nowaja-Semlja och Je- 



nissej insaml. hafs-mollusker; K. Sv. Vetensk.-Alcad. Handl. Bd. 16, Nr. 2, 



1878, p. 19, Tab I, Fig. 4 a— с. 

 ^) Posselt: Østgrønl. Mollusker; Medd. om Grenland, XIX, 1895, p. 71, 



Tab. I, Fig. 8-12. 

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



Forhandl. Bd. 23, 1901, p. 304 («Astarte arctica^). 



