Larcis
The Arcis or Larcis (with article agglutination; ) is a river in Southwestern France. It is a  right tributary of the Léez, originating in the commune Luc-Armau in the east of the Pyrénées-Atlantiques. It joins the Léez in Lannux, in the French département of the Gers. It is  long. Name 
The name is documented as Arsiis (1540), Arciis (1542), Arcis (1863). The name of the Arcison, a left tributary of the Layon, is related. Main tributaries 
 (L) Lizo, 
 (L) Léès, from Saubole. References

Rivers of France
Rivers of Gers
Rivers of Pyrénées-Atlantiques
Rivers of Nouvelle-Aquitaine
Rivers of Occitania (administrative region)