I9I5- ^O- 12. THE STROPHOMEXIDAE OF THE KRISTIANIA REGION. 4I 



the length, with rather pointed cardinal angles. X'entral va!ve very slightly, 

 evenly, convex: dorsal nearly flat. Greatest elevation in the umbonal 

 region. 



Radiating striation excedingly fine, so fine that it is not seen without 

 difficulty with the naked eye. The striae, the number of which increases 

 towards the latero-fi-ontal margin bj* interpolation are quite or nearly equal 

 in size; at places where the3- are not exactly alike, they vary without 

 regularity, at least two distinct types cannot be found. Besides the radi- 

 ating ribs, faint but never failing concentric undulations are present. They 

 are strongest near the hinge, where thej- point strongly outwards, forming 

 a very acute angle with the hinge, especially in the lateral part of the 

 shell. Anteriorl}' the}- are often so faint that they are only obser\ed 

 with difficult)-. 



Interior not known. 



Observations. With its flatness and fine striation this form 

 approaches Strophomrtia (Leptostrophia) filosa Sow. from which form, how- 

 ever, it distinctly differs in some respects. Without knowing the exact 

 outline of the form it is evidenth" much broader in shape than the British 

 species, that according to the illustrations has an outline ver\- much like 

 that of Rafitiesquina expansa. Further the Norwegian specimens show a 

 faint concentric wrinkling not present in the British species, and finall}* the 

 radiating ribs of the former seem to be both more delicate and more 

 equal than in the 5. filosa. 



Occurrence. 6 (a — cl Sælabonn. Ringerike; Gunneklev, Skien- 

 Lansresund district 



Leptostrophia ßlosa Sow. var. lata n. var. 

 (PI. II, fig. 15—16.) 



Mat. pres. An outer mou'.d of a dorsal, two inner casts of ventral 

 valves, all verj- fragmentary. 



Description. The exact outline cannot be seen in anv speci- 

 men; from what is to be seen, however, it is evident that we have here 

 a ver}' broad Strophomenid, the width being about double the length. 

 The cardinal angles do not appear, however, to be ver\- sharp. Both ventral 

 and dorsal valves are nearly flat, the principal convexity (concavity) being 

 found in the median line, and especially at the beak, as can be judged 

 from the interior moulds of the ventral valves. 



