I9i=>- No. 12. THE 5TROPHOMEMDAE OF THE KRISTIANIA REGION. 69 



There is no doubt as regards the generic position of this species. 

 Besides the exterior with the coarse striation being that of a typical 

 Schitchertella, the interior of the dorsal valve with the prominent, straight, 

 fhort abruptly terminating crural plates, gives the same result, differing 

 srom that of Strophonietia (or Strophonella). 



Occurrence. 5 a. Bondibraaten. Asker Bærum ; 5 b. Ostre Svartø, 

 Ringerike. 



6 la — c), Loc. in Ringerike, Isl. off Holmestrand, 



Bundefjord, Skien-Langesund. 



7 (7 c), Malmø, Bundefjord 



8 (b — cl. Ringerike, Malmo. Isl. off Holmestrand. 



LeptaenR Dalman 1828. 



The range of this genus in the sense of Hall and Clarke, is extre- 

 mely small, being restricted to include forms with the type of internal and 

 external characters of L. rhomboidalis Wilck. 



The reason for allowing the generic terra Leptaena embrace this type 

 of Strophomenidae and not like Davidson forms like Lcptœna iransversalis 

 Wahl, now included in Plectambonites, is discussed b\- Hall and Clarke 

 in Pal. New York, VIII, i, p. 279 — 280. 



Leptaena rhomboidalis Wilckens. 

 (Pi. XII. fig. I — 12.I 



For European Synonomj' see: 



StrophoMiena rhoitibosdalis lWiLCK.1 in D.wnDSOx, Brit. Sil. Brach, p. 281. 

 For .American Synonomy see : 



Lepiana rhomboidalis <Wii.ck.) in Schchcebt. Sx-nopsis of .American Foss. Brach, 

 p 240. 



This most common of all Palæozoic Strophomenids is abundanth' pre- 

 sent also in the larger part of the sedimentary marine series of the Kri- 

 -•^tiania region, from 4 b upwards into Ludlow. 



As it may be of interest for future studies on this form in other 

 regions, I will shortly mention the varieties occurring in each of our stages 

 separately. 



Stage 4. Figs. 4, 6, 8. Already from the lower part of 4 b. though 

 not from the very base, we have specimens, of L. rhomboidalis from dif- 

 ferent districts. It seems however difficult to fix any certain variety to be 

 essentially characteristic of these oldest occurrences. The outline — as seen 

 from the central disc — varies very much. We have extremel}' broad 



