104 Billings on the age of the so-called Potsdam Rocks 
Table ie shooting the geographical and geological distribution of the species 
et this paper in Vermont and Belle Isle, so far as is known 
ae yt 
Geographical Geological 
distribution. distribution, 
Belle Isle.| Vermont. ypocemeey bere 
ee Scolithus linearis (Hall), * 
Pag pow * Paleeophycus i — 2 a *: 
3 “4 ongregatu ks 
bloc ® Archeoeyathus Atlantious x . 
€ Us:* Min nganensis, ‘ . * 4 
Gay * Obolus Labradoricus : 
Cr ae Obolella chromatica . 
ea. - “ _ cingulata #8 Mi 
is Orthis (undescribed) -- i 
10 * &“ * 
11 * “ +“ s“ * 
12 * Orthisinia ate nata = 
13 24 (un described) ” 
14 * “ * 
15 aed Cametella antiquata be 
1 707% _ Paradox ides Thompsoni (Hall, * 
17 # .. Vermontana “ = 
1Sih oMort= Conocopalite miser (Billings), - 
19 " Adamsii ~! 
20 . . Teucer & - 
21 . . aeenie . * 
22 * “ renceus | @ * 
23 i Bathyurus snes ss sed 
25} .-* Salterella rigs - He 
3 Aig obtu “ * 
27 = # paldhetté “ a 
Upon the above table I beg to make the following remarks: 
he two genera of trilobites Paradomides and Conocepholites at 
undoubtedly Primordial types. Bathyurus makes its first af 
seo in the snrneem group, is most abundant in the Caleifer- 
us sandrock, and becomes extinct in the lower - of t 
Pentel, where it is represented by one rare species, B. spiniger; 
the > Acidaspis spiniger of (Hall) Pal. N. Y., vol. i, p. 241, pl. 64 
OBOLELLA is a new genus closely allied to Obolus. There are 
four species known to me, one in the Potsdam of Wisconsit, 
another in the lies near Troy in — mir (ap parent 
either Calciferous or Potsdam) and the two mentioned in thé 
above a of these, O. sarge oe may Joonstivat a fort 
genus. ve posed to call sp Renepion: bs retain it for 
present. ‘eciGheaiia 3 
iil 
