Cyathaspidida are spindle-shaped extinct fish that lived near or in the bottom of the ocean floor roughly 420 million years ago. These interesting creatures were completely protected by armored plates, including a scaled tail. 

This particular specimen displays two pieces of the armored plates of Americaspis. 

Type: Jawless Fish (cyathaspids)
Species: Americaspis americana
Age: Silurian (443 - 416 million years ago)
Formation: Wills Creek Formation
Locality: Perry Co., Pennsylvania

Size (of whole plate): 2.75 x 2 x 1.25 inches
Size (of specimens): ~ 1.5 x 1 inches
Weight: 6.6 oz.