74 OLAF HOLTEDAHL. M.-N. Kl. 



The onl}' distinguishing character found in the exterior aspect of the two 

 forms is the broader and shorter outHne of the Norwegian one, and further- 

 more a differing size, the American L. iinicostata being considerably larger. 

 As the two Norwegian specimens found are of the same size, they probably 

 represent a mature stage of growth and not young individuals. Without 

 the interior of this form being known it is impossible to decide with cer- 

 tainty its relation to L. iinicostata. 



Occurrence. 4c. Railroad section at Flatla, Lunner, Hadeland. 



Leptaena sp. (cf. unicostata M. and W.). 

 (PI. XIII. fig. 2.) 



An interior mould of a ventral valve, the outer form of which has 

 certainly much resembled that of the form above mentioned from Hade- 

 land. It has been a fairly small, very broad specimen, strongly convex 

 longitudinally, roundly geniculated. 



The muscular area has been very strong!}' marked by surrounding 

 ridges, and the fairl}^ large diductor scars have been distinctly bilobed, for 

 the greater part of their length embracing the very elongate adductors. 



Observations. I consider it extremely probable that this speci- 

 men belongs to just the form described above. It is somewhat larger, but 

 corresponds very well in general form and is furthermore found in a 

 stratigraphical zone of a not very difterent age. 



The interior of this ventral valve certainl}' has much in common with 

 that of Leptaena iinicostata, only the muscular field is longer in that species, 

 its length being about -/3 of the total length of the valve. 



To judge from the illustration that Billings in »Palæozoic Fossils* 

 p. 118 has given of his species Stropliomoia nitens from the Hudson River 

 group of Anticosti, this form in exterior appearance is extremely like 

 the Norwegian specimens just described. In the Chapter on Brachiopoda 

 in »Paleontology of Minnesota« I, p. 413 Winchell and Schuchert also 

 emphasize the relationship between that form and Leptaena unicostata. 



Occurrence. 4b, low. part. Gravestranden, Frierfjord, Skien — 

 Langesund district. 



