I08 OLAF HOLTEDAHL. M,-N. Kl. 



While the Anticosti Strophomenids thus show several points of con- 

 nection, those of the interior regions of North America are in general 

 totally different, when we do not consider the relatively long-lived, cos-, 

 mopolitan forms that have little interest as guide fossils. Of other species 

 that occur in identical or related forms the following may be mentioned: 



A Stroph. pseudodeltoidea — like (yet smaller) form, which by Foerste has 

 recently been separated from S. flucliiosa as a distinct variet}' occidentalis, 

 occurs in the Richmondian of Minnesota. A somewhat similar form is S. 

 trilobata Owen from the middle Galena of Minnesota (also known from the 

 Trenton of Iowa and Manitoba) a species that shows much likeness to 

 our 5. rigida var. frognooisis from 4 d. The surface characters may, 

 however, be somewhat different in the two forms. Stroph. Keilhaui from 

 5 b is eceedingly like .S. nutans Meek from the Waynesville of the Rich- 

 mond of Ohio and Indiana. -S. Scofieldi W. and S. occurs in the Chri- 

 stiania region in the upper part of 4 b, in Minnesota (and Wisconsin) near 

 the base of the Galena shales. S. Kiœri occurs in 5 a, the rather similar 

 S. vetusta James and S. neglecta ^) James in the Waynesville of the Rich- 

 mond. 



Of Ordovicic Rafmesquinas we have the R. deltoidea from 4 b, (the 

 identification being however only based on exterior characters), occurring 

 in the Trenton and Utica of North America, R. cf. alternata loxorhytis 

 from the upper part of 4 b, the American typical form cited from the 

 Lorraine. 



Leptaena unicostata occurs in America in the Lorraine, a very similar 

 form high up in 4 c in Norway. 



In America the Strophomenids in their tirst fairly rich development 

 appear in the Chazy, a zone that may be considered about synchronous 

 with the one, in which the Norwegian forms are first met with, 3c. 

 Already from this old time the fauna has an aspect different from the 

 North European one, and this difference does not diminish later on. As 

 the development of the Strophomenids has thus gone along different lines 

 in America and Europe, we encounter great difficulties in trying to 

 use these fossils for correlation purposes and I will not here go into that 

 question, which however 1 hope to consider on a future occasion. What is 

 indicated rather strongly is a likeness between the Strophomenid fauna of stage 

 5 and the Richmond of North America. As to the older zones, we have 



^ It is quite a peculiar circumstance that just at this time, viz. near the end of the Ordo- 

 vicic period, we find in a number of forms a tendency to the development of the short 

 wrinkles near the hinge line, that is always found in the Norwegian form last mentioned, 

 and very commonly in the American ones. The same feature is found also in another 

 form from 5 in Norwaj', viz. Raf. pseudoalternata Schmidt. 



