Ig2 UNIVERSITY OF COLORADO STUDIES 
miles north of Boulder. Inthe Arkansas Valley it is reported from about the same horizon, 
but the Denver Basin monograph credits it to the upper Pierre, where it is also found on 
the Yellowstone River (Meek). 
Ptychoceras sp. 
We found one example at Fossil Ridge, undeterminable specifically. From three 
to eight miles north of Boulder P. crasswm White and P. mortoni M. and H. are found just 
above the Hygiene sandstone. 
Baculites ovatus Say 
Of this species, which is abundant from Boulder to the Little Thompson above, below 
and in the Hygiene sandstone, we have found but three or four examples, yet curiously 
enough Dr. White reported this species from Fossil Ridge and omitted B. compressus Say, 
which is abundant there. The species ranges through the Pierre and into the Fox Hills. 
Baculites compressus Say 
Abundant at Fossil Ridge, but rather uncommon in the Boulder District, where, 
however, it has been found both above and below the Hygiene sandstone. 
Scaphites nodosus Owen 
Found occasionally in the Hygiene sandstone from the south end of Lake Loveland 
to Rocky Ridge. Inthe Boulder District it is found both above and below that sandstone. 
In the Denver Basin monograph it is credited to the lower Fox Hills. On Yellowstone 
River it is found in upper Pierre (Meek). 
Scaphites nicolletii Morton 
We have collected four specimens on Fossil Ridge, the only ones we have seen in the 
state. It is reported from the Fox Hills formation on the Yellowstone River, etc. (Meek). 
Placenticeras whitfieldi Hyatt 
This large species is common on Fossil Ridge, but is usually found in fragments. 
In Dr. White’s list on page 177 of his report it is given as “ Placenticeras placenta var. 
DeKay sp.,” but in the text of the same report at page 186 “‘ Placenticeras lenticulare 
Owen sp.’’ is mentioned from the same place, doubtless referring to whitfieldi, which he 
could hardly have overlooked. A large number were found above the Hygiene sandstone 
three miles north of Boulder. 
Placenticeras intercalare M. and H. 
We have but one example from Fossil Ridge—a small one. We also have one from 
the base of the upper third of the Pierre three miles north of Boulder, one from the very 
top of the Pierre (as its limits are understood in northeastern Colorado) at the mouth of 
the St. Vrain, and one from the upper Fox Hills four miles southeast of Windsor, all only 
a few inches in diameter. 
PISCES 
Lamna sp. 
We have a single shark tooth, specifically undeterminable, from Fossil Ridge. 
