94 OLAF HOLTEDAHL. M.-N. Kl. 



minent ridges in the interior of the dorsal valve this form reminds one 

 considerably of Plectella and Strophoiuciia (?) Ncfedjeivi, to both of which 

 it probably is fairly closely related. R. imbrex may well be regarded as 

 a primitive form out of which many of our later Rafinesquinas have 

 developed. It is much to be regretted that I do not know the dorsal 

 interiors of these forms from stages 4 and 5, so that their relation to 

 R. imbrex in that respect cannot be considered, hi the British form from 

 Caradoc, which Davidson called Strophomena deltoidea Conrad ^ which, 

 however, by Winchell and Schuchert - is considered to be different in 

 interior characters from the American form and which may be closely 

 related to our Raf. psendoalternata Schmidt, we find, as depicted by 

 Davidson, a dorsal interior which reminds one strikingly of R. imbrex. 

 It is of interest that a dorsal interior much like that in R. imbrex is found 

 in a very old North American Strophomenid, Lepfama (?) iiicrassafa Hall-^. 



The Rafinesquinas from 4 and 5 show man}' different types as to 

 external appearance. We have strongl}' geniculated forms like Raf. Pan- 

 deri, R. psendoalternata Schmidt and more evenly convex, less curved 

 ones like R. carinata and R. cf. cormgatella Dav. Further, we have 

 strongly corrugated types like R. (?) semipartita. 



Raf. cxpansa Sow. which becomes the dominating form in the lower 

 halt of the siluric may have its nearest relative in older Rafinesquinas in forms 

 like the Raf. sp. (p. 23) and R. cf. R. alternata loxorliytis Meek from stage 4 of 

 the Mjesen region. The latter form is the only one which 1 think can be con- 

 sidered with certainty as a Norwegian representative of the R. alternota 

 group, so exeedingly common in the upper Ordovicic of North America, 

 a group to which R. expansa is exeedingly closely related. The form 

 has the large, striated ventral diductor scars, which are found in both 

 R. alternata and, — though less developed, — in R. expansa. 



A good number of forms with a more or less peculiar surface orna- 

 mentation have been referred to Rafinesqinna onl}- with doubt, many of 

 them showing in exterior chararacters (the interior is not known) a con- 

 siderable resemblance to Lcptaena. These forms that have generally been 

 tound in one specimen onl}', are to be regarded as rather highly specialized 

 types, most of them standing very isolatedly. Thus for instance the beautiful 

 Raf. (?) ringerikiensis and the large R. (?) Schnndti Gagel. The Rafmes- 

 quina{?) sp. from 8 (see p. 31) strongly reminds one of R.i?) cf. elegans 



1 Brit. Sil. Brach., pi. XLII, figs. 1-5. Suppl. pi. XV, figs. 16-22. 

 - See Paleontology of Minnesota, I, p. 404. 



^ See P. Raymond on „The Brachiopoda and Ostracoda of theJChazy", Ann. Carnegie 

 Mus. Vol. VII, No. 2, 191 1, pi. XXXI V, figs. 33 — 35. 



