1915- No. 12. THE STROPHOMENIDAE OF THE KRISTIANIA REGION. 29 



Raßnesquina JJünsteri n. sp. 

 (PI. Ill, fig. 8.) 



Mat. pres. A single but nearly complete ventral valve in rock. 



Description. Shell of medium size, outline semi-elliptical, car- 

 dinal angles not projecting, only slightly less than 90''. The valve has a 

 narrow, deflected antero-lateral margin, the length (width) of which in the 

 median line is about ^ ^ of the length of the central disc. The latter is 

 slightly convex, flattening out towards the cardinal angles. 



The radiating ribs are of different sizes, a number of 4 — 8 finer ones 

 usually coming between two stronger ones. The latter are. however, in 

 different portions of the surface of very different strength, those situated 

 in the median part being very prominent, the size decreasing laterally. 

 The radiating ribs are crossed by very fine, very crowded regular con- 

 centric lines. A peculiar character is given to the shell b\- the alternating 

 depressions and elevations of the surface that are seen in the intervals 

 between the stronger radiating ribs, those of neighbouring intervals generally 

 not corresponding, so that no concentric continuous wrinkles are produced. 

 This undulating surface of the intervals is more marked in the median and 

 frontal portion of the valve than in the region of the cardinal angles. 



Observations. This form has a considerable resemblance to 

 Strophomena (Rafinesqiima) corntgatella Davidson but differs distinctly by 

 possessing a well-marked deflected margin, the British species being evenly 

 convex. The character of the wrinkles also is somewhat different. 



The name of this form is given in honor of Tho.mas Münster, Nor- 

 wegian Superintendant of Mines, who made many fine collections of fossils 

 from the Kristiania regions besides having given important contributions 

 to the geology of other parts of Norway. 



Occurrence. 4b (transition 4 b « — 4 b j) Bratterud, Ringerike. 



Raßnpsquina cf. corrugatella Dav. 

 (PI. IX, fig. 7.) 



Strophomena corrugatella D.w. Brit. Sil. Brach, p. 304, pi. XLI, figs. 8—14. 



A few outer moulds of small, sub-semi-circular dorsal valves, which have 

 been slightly and evenly concave, with radiating ribs of two sizes, 5 — 10 

 finer coming between each pair of stronger, approaches this British species. 

 Faint, irregular short wrinkles are seen in some places, being, however, of a 

 different type than in R. corntgatella. 



Occurrence. 5a, Stavnaestangen, Ringerike. 



5 a. Hero, Skien — Langesund district. 



