Sminthurides pseudassimilis is almost identical in appearance to Sminthurides signatus. The only difference is in females in the relative lengths of the four subsegments of the fourth antennal segment. In Sminthurides signatus, the first and fourth subsegment are about the same length whereas in Sminthurides pseudassimilis, the first subsegment is about twice as long as the fourth subsegment (at the tip of the antenna). Males of the two 'species' can not be separated.
The only specimen of Sminthurides pseudassimilisin the NMHL slide collection was found by Harold Gough in Cobham, Surrey in April 1965. The specimen is in fairly poor condition although the relative lengths of the fourth antennal subsegments are visible and fit the description above. However, the relative lengths of the fourth antennal subsegments of some of the specimens of Sminthurides signatus that I have seen are quite variable and there must be some doubt as to the status of Sminthurides pseudassimilis.