12 



OLAF HOLTEDAHL. M.-N. Kl. 



DESCRIPTION OF THE FOSSILS. 



It would carry us too far in this paper dealing with a group of brachiopods 

 of a certain region, to go into detail as to the delimitation and definition 

 of the systematic term Strophomenidae given by various authors, since the 

 name was established for a family of brachiopods by W. King in 1846. 

 In fact in this question the views of paleontologists have greatly differed, 

 and still differ. The large German text-books of paleontology for instance, 

 still contain the term Strophomenidae in the wide sense of King, embracing 

 beside Strophomena and allied forms, also Orthis and related genera. In 

 opposition to this view we have the newer system of the American paleon- 

 tologists, who have adopted S. P. Woodward's term Orthidac, making this 

 a family name for Orthis and nearly related forms, and thus largely 

 restricting the range of the term Strophomenidae. It is in this restricted 

 sense that the name will be employed in the present paper. 



This restriction is only one of the many that have been found neces- 

 sary in the revision of the classification of the brachiopods that was under- 

 taken by a series of skillful American paleontologists, and that was a 

 natural consequence of the enormous progress in the study of fossil bra- 

 chiopoda, that is connected with the names Hall, Clarke, Beecher, 

 ScHUCHERT, Walcott and others. In this revised classification, the Stro- 

 phomenidae and the Orthidae, on account of distinguishing characters of 

 considerable systematic value, above all the different character of the del- 

 thyrium, — this being generally open in the Orthidae, closed in the 

 Strophomenidae, — were naturally placed as two independent but related 

 families. 



Hall and Clarke, in the table of classification that is found in Vol. II 

 of their fundamental work: »An Introduction to the Study of the Genera 

 of Palaeozoic Brachiopoda« ^ (p. 353 etc.) have gone still further, having 

 made two families out of the Strophomenidae in the restricted sense. They 



1 Palæontology of New York VIII, 1892 — 94 



