I guess that is the correct ports version string.

2008-04-14 18:38:16 +00:00 · 2008-04-14 18:38:16 +00:00 · ad979a9a81
--- a/2
+++ b/2
@ -29,7 +29,7 @@ For Linux, download and extract the {libmemcached tarball}[http://download.tange
  make && sudo make install
  
 For OS X, you may be able to install it from MacPorts:
-  sudo port install libmemcached @0.19_0
+  sudo port install libmemcached @0.19
  
 Now install the gem:
  sudo gem install memcached --no-rdoc --no-ri