22 



OLAF HOLTEDAHL. M.-N. KI. 



alternata is beyond doubt, as I have among my Russian material, an 

 exactly corresponding specimen, labelled by Schmidt himself under that 

 name. In the name, Schmidt has indicated the resemblance to the common 

 American species Rafinesquina alternata, which however is easily distin- 

 guished by larger size and by different surface characters, especially the 

 lack of the well-expressed corrugations at the hinge line, etc. This feature 

 also distinguishes the form from related Norwegian species. 



Occurrence. 5a — b. Stavnæstangen, Østre and vestre Svartø, 



Ringerike. 



Rafinesquina sp. (cf. R. alternata Em. var. loxorhytis Meek). 



(PI. I, fig. 12.) 



1873. Strophoniena alternata var. loxorhytis Meek. Pal. Ohio, Vol. I p. 91. 



A couple of very badly preserved, greatly worn valves, one of which 

 can be determined as ventral, in several characters strongly reminds one 

 of that variety of the common Rafinesqiiuia alternata Em., being however, 

 much inferior in size to that very large form. Width of the specimen 

 with best preserved outline = 40 mm., length 23 mm. It has a similar, 

 rather broad outline with the lateral margins diverging more posteriorly 

 than in R. alternata, the convexity also being greater than in that species, 

 if not so marked as in more convex specimens of R. loxorhytis. 



It is an interesting fact that whilst the ventral muscular area in an- 

 other Norwegian form externally resembling Raf. alternata and allied 

 species, viz. Raf. mjøsensis, was found to be very different from what is 

 seen in that American form, the ventral muscular scars in the form in 

 question, as they can faintly be seen in one of my specimens, are of the 

 type characteristic of R. alternata and related forms, large, without distinct 

 ridges around and crossed by a radiating striation. As to the surface 

 characters of the valves, the radiating ribs are of two sizes, rather regularly 

 arranged, the intervals between the stronger ribs near the front being on 

 an average 1^/2 mm. 



Occurrence. 4b, Coelosphæridium horizon. Fangberget, Mjesen 

 district. 



Rafinesquina parva n. sp. 



(PI- I, fig. 7-) 



Mat. pres. A single, incomplete ventral valve and fragments of 

 a few dorsal valves in rock. 



Description. Small (all specimens are of about the size of the 

 one depicted), semi-elliptical in outline, cardinal angles about 90°. The 



