Correspondence. 125 
Turtles. Plesiosaurs. 
Vomer unpaired. Paired vomers. 
No posterior parasphenoidal A separate parasphenoid. 
process. Opisthotic not separate. 
Opisthotic separate. Cervicals from thirteen to sev- 
Cervical vertebrae eight, enty-six. 
Ribs intercentral in attachment. Ribs diapophysial in Attachment. 
Ten dorsal vertebrae. Twenty dorsals. 
Dr. J. H. McGregor maintained that the Ichthyosauria belong 
to the Diapsida and that the closed condition of the temporal roof 
is secondary in nature. Dr. O. P. Hay showed that the original 
condition of the temporal region was a covered one, as shown by 
the skulls of the primitive Amphichelydia, all the older genera of 
turtles, and the lower families of living turtles. The roof has be- 
come reduced through excision from behind in most cases; from 
below, in others. There has never been any true supratemporal ' 
fossa. The turtles have been derived from the Cotylosauria, pos- 
sibly through the Chelydosauria. He maintained that the turtles 
and the plesiosaurs are so different that they belong to different 
subclasses. 
A paper was read for Dr. F. B. Loomis on "The Amherst col- 
lege expedition to the Wasatch and Wind river basins in 1904." 
New localities for vertebrate fossils were found and some interest- 
ing forms were obtained. Mr. O. A. Petersen reported on some 
investigations in the region where Daemonelix is found. He con- 
cludes that the fossil is the burrow of the rodent Steneofiber. Mr. 
Earl Douglass sent a paper and drawings describing a monotreme- 
like mammal from the White River beds of Montana. Prof. W. B. 
Scott gave a most interesting talk on South American ungulates. 
He presented a classification of the Notungulata and gave the char- 
acters of the divisions. None of these ungulates possessed horns. 
Dr. O. P. Hay presented a paper entitled "On the group of fossil 
turtles known as the Amphichelydia." This was based on a fine 
skeleton of Compsemys plicatula from the Jurassic of Wyoming 
and several good skeletons of Baena from the Bridger beds. This 
group, founded by Lydekker, is thoroughly established. There can 
be no doubt that it gave origin to the Cryptodira and the Pleurodira. 
Extremely interesting papers were read by Dr. Wm. Patten and 
Mr. W. J. Sinclair, the former on "The structure of the Ostraco- 
derms," the latter on "The Marsupials of the Santa Cruz formation." 
Dr. Patten exhibited a splendid collection of specimens of Both- 
riolepis. Dr. M. S. Farr reported on the discovery of many mam- 
mals in the Fort Union beds of Montana. Prof. S. W. Williston 
reported on an important locality for Triassic vertebrates near Lan- 
der, Wyoming. Many fine remains of labyrinthodonts were obtain- 
ed; also of dicynodonts, hitherto net found in America; four skulls 
of phytosaurs; and other remains not yet determined. 
Dr. E. C. Case read a paper entitled "Characters of the Chely- 
dosauria." He has discovered that Cope's genus Diadectes really 
