Some notes on the Mermaid crest:
The Mermaid was a badge of the Berkeleys, and Sir Walter Scott's dexter supporter. She figures, with the customary mirror and comb, in thr arms of Birmingham University as an emblem of the Mason family.
Source:
Boutell's Heraldry - J.P. Brooke-Little - 1983
The Mermaid , is much more frequently met with. It is generally represented with the traditional mirror and comb in the hands. It will be found appearing, for example, in the arms of Ellis, of Glasfryn, co. Monmouth. The crest of Mason, used without authority by the founder of Mason's College, led to its inclusion in the arms of the University of Birmingham. It will also be found as the crest of Rutherford and many other families.
Source:
A Complete Guide to Heraldry - A.C. Fox-Davies - 1985
There are three possibilities shown in Elven's Heraldry, those of O'Bryne, Myers, and Ellis:
On the above three examples, and Pat's example the mirror and comb are held in opposite hands.
Period sources such as Elven's are always my favoured choice, although often incorrect when compared with modern works, the fact that they were considered correct at the time, is the important thing, and would have been the source, and others like it, from which period engravers would have worked from.
Trev.