Phylum: Charophyta   Family: Desmidiaceae

Cosmarium contractum var. incrassatum  A.M. Scott & Prescott

Differs from the nominate with semicells that are mushroom shaped with the widest part below the centre. Status unknown for the Outer Hebrides

References: 
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland
Kouwets, F.A.C. (1999) A check-list of desmids (Chlorophyta, Zygnemaphyceae) of France