La medusa portland cement compañia. 

 - Cleveland-US :   Medusa Portal Cement Company,   1931. 
 - páginas 1-2 
 - Irregular 
 - Vol. 2, no. 10(Nov. 1931) 
 - Bolet¡n Medusa ;   no. 10 .
 - Medusa Portal Cement Company. .