The latest legal twist in the transatlantic custody case of the twin 8-month-old girls who were adopted on the Internet took place in an Arkansas courtroom Tuesday, when Judge Mackie Pierce declared the adoption invalid. The girls were adopted in Arkansas on Dec. 22 by a Welsh couple, Alan and Judith Kilshaw, which set off a dispute with an American couple, Richard and Vickie Allen, who had also tried to gain custody of the children through the same Internet adoption broker. (The Allens said they paid $6,000 in the deal; the Kilshaws, $12,000.) Judge Pierce has now ruled that neither couple met the 30-day Arkansas residency requirement. He is also asking that British courts return the girls to the U.S., a lawyer for the twins' natural father told the Associated Press.