SS 
Lower Potsdam Rocks at Troy, N. Y. 137 
of Canada to the Potsdam group, the conglomerates of which 
have afforded several of the species found in the Lower Pots- 
dam at Troy, as well as several occurring in the Lower Pots- 
am of Vermont and Labrador, with many others. The exact 
age of the formation holding these conglomerates is not yet 
positively settled; but it is, by Mr. Billings, regarded as at 
least not far from that of the Potsdam. 
The fauna of the Troy limestones appears to me to supply in 
_ a long-recognized blank in the Paleontology of our State. 
he Primordial fauna with us has hitherto been a meager one, 
being confined, with the exception of Scolithus, to the few spe- 
cies found in the Potsdam sandstone at Keeseville, Essex 
Descriptions of new species of Fossils from the Lower Potsdam 
group at Troy, :€ 
Microdiscus speciosus, sp. NOV. 
_ Description.—Head destitute of eyes and sutures, semi-ellip- 
tical, with a conspicuous border all around, thickened at the 
edge, which in the majority of cases carries from 5 to 6 minute 
tubercles on eac - border expanded in front. Glabella 
long, conical, prominent, smooth, without neck furrow, extet 
2 ing in an obscurely triangular projection 
deep dorsal furrows, sometimes, though only 
UV 5 in very rare instances, obscurely lobed 
‘ "Preto, Head; Posterior angles narrowly rounded. 
. e 
figured belong to two pointed, strai 
“ferent individuals. indi are bent down and slightly recurved, 
deeply grooved for nearly their whole length. The rings of 
the axis have a slight groove across them in the posterior half 
ofeach. The fourth or hindmost ring appears to be anchylosed 
