Twait shad are silvery, sometimes with a bronzy tinge, and there are a distinctive row of six to ten large dark spot just behind the gill cover though these may fade when the fish is dead. The adult length is typically . The twait shad is found in most of Europe and all countries bordering the Mediterranean Sea. "Alosa fallax" has a similar lifecycle to "A. alosa" (allis shad). They are known to live in sympatry. Some studies have suggested "A. fallax" and "A. alosa" species can hybridize. They are anadromous species, like many other species in the genus "Alosa". However, some
Subterranean river many cities there are natural streams which have been partially or entirely built over. Such man-made examples of subterranean urban streams are too numerous to list, but notable examples include: Some fish (popularly known as cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes. Greek mythology included the Styx, Phlegethon, Acheron, Cocytus, and Lethe as rivers within the Underworld. Dante Alighieri, in his "Inferno", included the Acheron, Phlegethon, and Styx as rivers within his subterranean Hell. The river Alph, running "Through caverns measureless to man / Down to a sunless sea" is central to the