PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 



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SMITHSONIAN INSTITUTION 

 U. S. NATIONAL MUSEUM 



Vol.108 Washington : 1958 No, 3391 



PYCNASPIS SPLENDENS, NEW GENUS, NEW SPECIES, A 

 NEW OSTRACODERM FROM THE UPPER ORDOVICIAN 

 OF NORTH AMERICA 



By Tor 0rvig^ 



Introduction 



In this paper a short description is given of a new ostracoderm, 

 Pycnaspis splendens, new genus, new species, from the Upper Ordo- 

 vician of the eastern slope of the Bighorn Mountains in north-central 

 Wyoming. This new form is related to Astraspis desiderata from the 

 Harding Sandstone, but it differs from the latter in the shape and 

 microstructure of the tubercles of the exoskeleton. At the type 

 locality it is associated with Astraspis? sp. indet. and Eriptychiida 

 gen. and sp. indet. Exoskeletal plates referable to Pycnaspis, new 

 genus, but at present indeterminable as to species are represented in 

 the Winnipeg formation of the Williston Basin in Montana and in 

 the Whitewood formation of the Black Hills in South Dakota, but 

 such plates are missing entirely in the Harding Sandstone of Colorado. 



Ordovician vertebrates from North America were first recorded by 

 Walcott who, in 1892, described small exoskeletal plates of two forms, 

 Astraspis desiderata Walcott and Eriptychius americanus Walcott, 

 from the Harding Sandstone outcrops near Canyon City, Colo. These 

 two forms Walcott referred tentatively to the Asterolepidae and 

 Holoptychiidae, respectively, but they are now generally recognized 

 as true representatives of the Heterostraci. Walcott also figured a 

 third fossil from the Harding Sandstone, Dictyorhabdus prisons Wal- 



1 Curator, Department of Paleozoology, Swedish Museum of Natural History, Stockholm. 



