The Xindi-Reptilian ray gun was a type of hand-held weapon occasionally carried by Xindi-Reptilian officers.
Xindi-Reptilians who traveled back in time to 2004 Detroit, in an attempt to create a bioweapon, were equipped with such hand-weapons. Loomis, a resident of that century, later referred to the weapons as "ray guns," upon being arrested by police officers from Detroit Police Department. (ENT: "Carpenter Street")
These firearms were also used by Reptilians aboard the Xindi weapon, shortly before its destruction. (ENT: "Zero Hour")
The name for these weapons comes from Loomis' reference to them.