Yukoniidae are typically isopygous, belonging to the Superfamily Eodiscoidea. The narrow glabella is usually parallel sided, anteriorlyrounded and separated from smooth anterior border by broad preglabellar field which occupies about 25% of cephaliclength excluding occipital spine. Posterior glabellar furrows are reduced to a pair of slits low on sides of glabella and directed backwards. Occipitalring bears a strong backwardly directed spine. Yukonia intermedia Palmer has three thoracic segments, the anterior of which has strong backwardly directed pleural spines. Pygidium of Yukoniidae has an axis of three to seven rings.