Geophagus are usually identified using a combination of body and fin markings: lateral bar quantity and pattern, infraorbital stripe (or lack thereof), pre-opercular mark, mid-lateral spot (on the side of the body), and patterns in the caudal fin. Dean Hougen drew up some pictorial guides to go with an article he wrote about Geophagus identification. These do not include several of the newly named species, but you can see altifrons and surinamensis. The big difference with juveniles comes down to the size of the mid-lateral spot. On altifrons it's very small, and as the fish grow to adulthood it it ends up only covering a couple of scales. Sometimes it disappears completely. As you can see in the illustrations, surinamensis will supposedly have a spotted caudal fin, while the altifrons is a mix of spots and stripes. Dean warns not to base juvenile ID off of this feature because the tail pattern can change as the fish matures.