SUPPLEMENT. S2S 



REjVE-A^RKS 



UPON THE 



TRILOBITES OF THE SHALES OF THE HUDSON-RIVER GROUP, 



WITH DESCRIPTIONS OF SOME NEW SPECIES OF THE GENUS OLBNUS. 



The Trilobites most common in the shales of the Hudson-river group are 

 Triarthrus beckii and Calymene senaria = Calymene blumenbachii ? I have 

 likewise described two species of Olenus in the first volume of the Pa- 

 laeontology of New- York ; but these are rare in most localities of the 

 rocks of this period. 



Some years since, during the progress of the Geological Survey of 

 Vermont by Rev. Z. Thompson, some specimens of Trilobites were obtained 

 from the shales of this age in the town of Georgia ; and these were sub- 

 sequently placed in my hands. The Survey having since passed under the 

 direction of Professor Hitchcock, I postponed the publication of the de- 

 scriptions, fearing it might not be agreeable to him ; but having now not 

 only his approval, but his express desire that I would publish them, I 

 give below the following species, preliminary to a more complete de- 

 scription and illustration. 



Olenns thompsoni ( n. s.). 



General form ovate, the length and breadth being nearly as six to five. 

 Head broad lunate, with the postero-lateral angles much extended ; the 

 width from the centre to the outer margin of the eye almost equal to 

 the width of the cheek. Eyes (which are much crushed in the speci- 

 men) elongate semioval, equal in length to the space between the 

 anterior angles and the frontal margin : glabella distinctly lobed, 

 narrower in front. 



