58 OLAF HOLTEDAHL. M.-N. KI. 



Observations. Although Barrandes Stroph. rigida with which 

 the Swedish Stroph. arachnoidea, described almost at the same time, must 

 be considered identical, is an almost flat, only slightly concave form, 

 the Norwegian specimens certainly must be referred to it. I consider the 

 flatness of both the Bohemian and Swedish specimens (of the latter I have 

 seen a number) to be a secondary feature due to pressure. As mentioned 

 above, the Norwegian specimens in shale are practically flat and cannot 

 in any character be separated from the other ones. 



Occurrence. 4 b (4 b a, ß, å) Asker — Bærum; (4 b y) Ringerike. 

 4c Hadeland; Ringerike; Asker — Bærum; Skien— 

 Langesund district. 



Strophomena, rigida, Barande. var. frognöensis n. var. 

 (PI. X, fig. 5.) 



A single dorsal valve with exactly the same surface ornamenta- 

 tion as the specimens just described, differs so distinctly in general 

 form that it must be kept separate. The outline is much more triangular, 

 the lateral margins meeting at a rather sharp angle at the front. 



The cardinal angles are not fully preserved but have certainly been 

 about 90 ^' or somewhat more. Another differing character is the rela- 

 tively very strong convexity of the valve, the gibbosity being fairly regu- 

 lar, with greatest elevation at about the centre. 



Occurrence. 4d, Frognø, Ringerike. 



Strophomena antiquata Sow. 

 (PI. X, fig. 6—10.) 



Synonomy see Strophomena antiquata Sow in Davidson, Bril. Sil. Brach, p. 299 



Without having an opportunity of studying the whole British material on 

 which Sowerby and Davidson have founded this form, it is rather difficult 

 to understand what is really meant by it. Sowerby's original type speci- 

 men was a very small shell, certainly a young individual with a few very 

 sharp and prominent radiating striae. In 1847 Davidson describes a form, 

 that he calls Strophomena scabrosa, which however, later on, he considers 

 to be only the mature form of Sowerby's small specimen of S. antiquata ^. 



1 In Davidson's paper : Mémoires sur les brachiopodes du système silurien supérieur 

 d'Angleterre, Bull. Soc. Géol. France. 2 Sér. Vol. 5, 1848, p. 318—310 he has kept 

 apart as two species Leptœna antiquata and Lept. scabrosa without going into detail 

 as to distinguishing characters. 



