54 



OLAF HOI.TEDAHL. M -N, Kl. 



and in surface characters approach the specimen, last mentioned, every 

 second or third rib being stronger than the others. 



Observations. The Strophomena lima Tornquist ^ from the 

 »Leptænakalk« of Sweden can probably hardly be separated from S. As- 

 must. A few fragmentary specimens kindly sent to me for comparison by 

 the late Prof Moberg of Lund, show in size, general form, and striation, 

 similar characters to our Norwegian specimens and a few Russian specimens 

 of 5. Asmusi that I have before me. 



Strophomena, Kiæri n. sp. 



(PI. IX, fig. 4-6.) 



1897. Strophomena nov. sp, Kiær, Faunistische Uebersicht d. Etage 5 des norwegischen 

 Sil ursy stems, p. 11. 



Mat. pres. A fairly large number of ventral and dorsal valves, 

 besides some broken free specimens present. 



Description. Shell of medium or rather large size, very thin, 

 outline regularly semi-elliptical, broadly rounded in front; posterior portion 

 of lateral margins parallel or very slightly divergent towards the hinge. 

 Cardinal extensions very small and not very sharp. Ventral valve slightly 

 and evenly concave without any convexity in the umbonal region except 

 at the very beak, which is somewhat elevated. Dorsal valve slightly and 

 regularly convex, following very closely the ventral one. 



The radiating striae are generally not very straight, rather irregular, 

 of two distinct sizes. The intervals between the stronger ribs are com- 

 paratively small, in the middle of the valves i mm. 

 or less, in each interval i — 3 minor ribs, that are 

 m' j ( often very delicate and difficult to see. The crowded 



concentric raised lines are generally more con- 

 spicuous, and in places may be very prominent, 

 „ ,,. J • r , The most characteristic surface marking is a small 



üuthne and section of a ventral ° 



valve of Strophomena Kiæri, number (usually 4 — 5) of very short wrinkles near 

 with outline of muscular field. ^^^ j^jj^g^ jj^g^ y^ese wrinkles are seen close 



to the hinge line only, reaching anteriorly from the hinge for about 3 mm., 

 where they gradually disappear. 



By taking away the shell substance of a ventral valve the muscular 

 field was shown to be of medium size, well marked by an elevated ridge, 

 except at the very front. A faintly elevated ridge has crossed it in the 

 median line. 



^ See Angelin- Lindstrøm Fragmenta sihirica, p. 29, pi XIV, fig. 43. 



