SUPPLEMENT. 
525 
EEMARKS 
UPON" THE 
TRILOBITES OF THE SHALES OF THE HI BSON-RIVElt GROUP, 
WITH pESCRIPTIONS OF SOME NEW SPECIES OF THE GENUS OLENUS. 
The Trilobites most common in the shales of the Hudson-river group are 
Triarthrus heckii and Calymene senaria = Calymene blumenbachii? I have 
likewise described two species of Olenus in the first volume of the Pa¬ 
leontology 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. 
Olenus 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. 
