Diclonius (meaning "double sprout") is a genus of dinosaur from the Late Cretaceous. It was a hadrosaur based solely on teeth. Its fossils have been found in North America. The name is in reference to the tooth roots, which are doubled and in contrast to Monoclonius ("single stem"), which Cope named in the same paper.
The type species, Diclonius pentagonus, is a nomen nudum discovered by Cope in 1876. Other formally undescribed species include D. calamarius and D. perangulatus. A "fourth" species has been reclassified as Anatotitan. They are all tooth taxa, known only from teeth and one jaw.
Although Cope referred several other batches of teeth to the genus, under several species, the name is considered a nomen dubium.
*Note: Diclonius mirabilis is actually the assignment of Trachodon mirabilis to Diclonius by Cope (1883).