868 The American Naturalist. [October, 
Ortmann believes that this is also the reason why so few 
forms of the Trapeziide are found in the West American 
region. After this he makes some very important remarks 
about the geological age of the Trapeziide. 
“The distribution of the Trapeziide also demonstrates an 
important fact, which is of significance for the consideration 
of the geological age of this family. While represented on 
the western side of America, it is totally absent from the east- 
ern side, especially in the West Indian Seas, so rich in corals. 
This fact is to be considered still the more, since the West and 
East American littoral regions show considerable relationship. 
This resemblance, however, must be explained by the former 
history of the American seas; that is, the well known and 
generally accepted union between the Caribbean Sea and the 
Pacific Ocean, which- existed in the middle of tertiary time. 
The fact that the Trapeziide were unable to migrate into the 
Caribbean Sea, indicates that the land connection between 
North and South America was already finished during the 
time of their origin or their immigration into the West Amer- 
ican littoral region, preventing their further eastern advance. 
From this reason we have to consider the Trapeziide as a 
relatively young family, which can not be older than the for- 
mation of this land barrier; that is, not older than Middle 
Tertiary (Miocene), but possibly still younger. 
“ Especially the Trapeziide indirectly prove that the rela- 
tions between the tropical West Indian and tropical Indo- 
Pacific faunas can only be explained by a connection in for- 
mer times, which does no longer exist, for they demonstrate 
that a group of animals, arising in the Indo-Pacific region 
after its isolation in its present form, and which seems to have 
the power to pass over extensive areas of the sea, was unable 
to reach the eastern American region. The Trapeziide could 
pass the barrier of the open Pacific and thus reach the west- 
ern coast of America, but they could not enter the Atlantic 
Ocean; on one side they were prevented by the Isthmus of 
Central America, on the other side they could not pass the 
southern point of Africa, which is doubtless caused by the 
prevailing conditions of temperature in that region.” 
