330 The American Geologist. "^"°^' ^®^^ 
Dr. Leidy, Prof. Cope, and the writer. All three have 
visited the region and made collections. Dr. Leidy described 
altogether thirteen species, ten of which must be regarded 
as well founded. Two of these ten were described in 1869; 
three in 1870; four in 1871 ; and one in 1872. Of Cope's 
twenty-four nominal species eighteen appear to stand the 
test of critical study. Twelve of these eighteen were_de- 
scribed in 1872; four in 1873; and two in 1884. Up to the 
present time the wMter has described a single species. He 
has in hand materials for the description of about a dozen 
more. 
Dr. Leidy and Prof. Cope were largely interested in the 
study of other groups of fossil vertebrates, and probably 
took no especial pains to secure good and abundant chel- 
onian materials. A few of the shells described by them 
were quite complete, but many of the species were based on 
very fragmentary specimens. 
In the year 1903, the writer, under the auspices of the 
Carnegie Institution, spent, in compan}^ with Mr. Walter 
Granger and Mr. Albert Thomson of the American Museum 
of. Natural History, nearly two months in the region of the 
Grizzly buttes and along the lower portion of Cottonwood 
creek. \Miile the others of the part}- were mostly engaged 
in collecting fossil mammals the writer gave especial atten- 
tion to the securing of fossil turtles. Great care was taken 
to secure good materials and to get the whole of every 
specimen discovered. As a result of this work, there were 
obtained about 140 specimens. Some. of these are indeed 
fragmentary ; but many of them furnish fine shells, some of 
them large portions of the skeleton ; and altogether about 
ten skulls were secured. Previously only one damaged 
skull had been brought from that region. Nearly the com- 
plete osteology of some species is now known which pre- 
viously were represented by their shells only. In several 
cases, species which had been based on fragments of the 
shells are now represented by much more complete mate- 
rials. 
Three superfamilies of turtles are known to have had 
representatives living in this Bridger basin, the Amphi- 
