The contradictions between the two descriptions of these creatures stems from the fact, that while protagonist of this story was doing some preliminary investigation into sightings of these creatures he had read the descriptions from multiple sources and locations.
“The creatures were sort of huge, light-red and crab like with many pairs of legs and with two great bats like wings in the middle of the back. They sometimes walked on all of their legs, and sometimes on the hindmost pair only, using the others to convey large objects of indeterminate nature.”
Chapter 1 Whisperer in Darkness, H.P. Lovecraft