Unfortunately, identifying Xanthotype species by external characteristics is problematic because they share the same characteristics, and the variation among individuals of a species is greater than the variation between species. See comments in the Remarks section on the Guide page for the genus.
The CBIF site shows 3 images of X. sospeta and 3 of urticaria. Just for fun, I arranged the 6 images in no particular order here and removed the names. If someone devised a key to differentiate these 6 specimens, the key would eventually break down when 60 - or 600 - specimens were examined; I think that's the point that Rindge makes in the Remarks section.