Just to clarify the example that I read...using your example...  The 
husband doesn't neccessarily have to take on the surname of his 
wife's father.  But in your example, you have a Carlos Garcia Mendez 
and a Carlita Garcia Mendez, two siblings.  Carlos gets married and 
has children and on his wedding records and his children's baptismal 
records he is referred to as Carlos Mendez, basically dropping the 
Garcia.  His children then become Jose Mendez Lopez, where Lopez is 
his wife's surname.  Carlita on the other hand, when she gets married 
and has children she is referred to as Carlita Garcia.  Her children 
are then Jose Lopez Garcia, where Lopez is her husband's surname.  So 
these two siblings end up having different surnames.

Thanks,
Angie.

P.S. Still looking for my source...

--- In ranchos@yahoogroups.com, "Jose  Macias" <usa20@e...> wrote:
> Angie;  Though I can see the logic of what you say you may have 
read, I have never seen this to be the case in taking the surname of 
the wife.  
>   As you know, the child of Hector Garcia and Rosa Mendez would be 
for example Carlita Garcia Mendez.  I have never seen a man change 
his name to Hector Mendez.  It is not true in Mexico, Central America 
or  South America, is it true maybe in Spain or Portugal ?  A family 
name is very important and I have never seen a case where a man would 
change his surname to that of his wife's father.  I wonder where you 
read this ? Traditionally the woman keeps her maiden name in that way 
even after marriage. 
>   I know about the variations in the spelling of names. I have seen 
some very strange attempts to spell Indian names by phonetics.
>   Anyway, I found your entry very enlightening and will remember to 
keep it in mind as I look over the records from now on.  If you will 
tell me where you have seen this practice, it would help me very much.
> 
> Jose L. Macias
> usa20@e...