1915« No. 12. THE STROPHOMENIDAE OF THE KRISTIAN'IA REGION. 25 



convexity, and also another character in surface ornamentations. The very 

 prominent ribs of first order, rather widely separated by fairly equal inter- 

 vals, filled with striae of greatly inferior strength, give the surface a rather 

 characteristic aspect. 



Occurrence. 4c, Gran, Hadeland. 



Raünesquina sp. (cf. Pt. alternata Em.). 



A broken and very strongly worn free specimen, that in outline and 

 convexity shows very much resemblance to that common American form, 

 being, however, a good deal smaller in size ^ — . 

 than average sized specimens of R. alternata. 



Cardinal area of ventral valve is fairly well ; /^ \ \ \ 



preserved and rather high, and stands a little \j I \ 



more vertical than in the American specimens V /11 



I have seen. Consequently' the relative thick- \ / / / 



ness of the Norwegian specimen also exceed ■"■"'^ 



what is ordinary in American ones. Raßuesqmna sp. fcf. R. aitemata 



" . ^ . . . Em. I. Outline, longitudinal section 



I O reach anv definite conclusion as to ^„ j ^, • • er 



-- and posterior view. Surface not 



specific relations with so poor a material is preserved, 



impossible. As far as I can see the specimen cannot be united with any 

 of the other forms described here. 



Occurrence. 5a, \'aker, Ringerike. 



Rafinesqaina, carinata n. sp. 



(PI. II, fig. 4-5-) 



Mat. pres. A number (about 10) of ventral valves and external 

 moulds of dorsal ones in rock besides a single incomplete free specimen. 



Description. Rather small, w'ith a nicely rounded semi-circular 



outline. Cardinal angles 60 — 70 ^. Proportion of width to length seems 



to be fairly constant, the dimensions of some specimen are given below 



in millimeters. 



Width 32 29 15 



Length 20 18 9 



\'entral valve moderately convex, having as a typical character a 

 distinct, rounded keel-like elevation in the median line, the surface sloping 

 for some distance rather sharply from this elevated portion to both sides, 

 then becoming more flat and finally reaching the lateral margins with 

 even and moderate convexity. Dorsal valve slightly concave, with a median 

 depression, corresponding to the keel of the ventral valve. 



