1915- No. 12. THE STROPHOMENIDAE OF THE KRISTIANIA REGION. 55 



An interior mould of a dorsal valve is depicted in pi. IX, fig. 4. 

 We see here roundedly triangular cavities, corresponding to the branches 

 of the cardinal process, further not broad, but rather deep depressions, 

 gradually disappearing laterally, corresponding to the crural plates and 

 finalh' a depressed median line reaching a short distance in front of the 

 cardinal process. On both sides and to the front of the median septum 

 there existed a series of narrow but strongl}' elevated ridges, that may 

 belong to the muscular field. Further in front rather faint vascular 

 markings are seen. 



Observations. The species here described comes fairly near 

 to Strophomena simulons M'Coy from the British Caradoc, a slightly con- 

 cave, very thin form of similar size and with wrinkles near the hinge 

 only. According to the description and illustrations given by M'Coy and 

 Davidson this species is relatively somewhat broader at hinge and deci- 

 dedh' more strongly concave in the antero-lateral portion. The intervals 

 between the major striae are larger, »every fifth, seventh, or ninth of the 

 striae larger than the others«, and the outline of the ventral muscular 

 field seems to be different. 



Sfrophoniena Kiœri somewhat resembles a group of American Stropho- 

 menas, common in the 3'oungest Ordovic, forms like S. neglccta James 

 and vS. vctitsta J.ames, these American forms however, generally having, 

 shells of larger thickness and somewhat coarser striation. 



Occurrence. 5a, \'estre Svarto, Ringerike. 



Strophomena Keilhaui n. sp. 

 (PI. \TI, fig. 8.) 



Mat. pres. About four ventral valves (partly as exterior moulds) 

 and a couple of dorsal valves, none being quite complete, besides minor 

 fragments. 



Description. Shell of small size, outline roundedly pentagonal. 

 No sharp projected cardinal extensions seem to have been present. \'entral 

 valve slightly (sometimes very slightly) concave, most strong!}- so at a point 

 nearer the beak than the front. At the very front there is a slight indi- 

 cation of a sinus. Dorsal valve moderately and rather evenly convex, highest 

 elevation at a point about -/5 the total length of the shell from the beak. 

 At the front, a faint fold. 



Radiating striae of no great strength; in the circumbonal half of the 

 valves the ribs are about equal, while near the rounded margin usually 



