>Please give us your opinion about the hinge and all that.<

It looks good for Donacidae, in agreement with the proposed identification.

>For the Isognomon, do you know a resource for such an ID ? These shells are not very sought after, and we miss infos on the web.<

I. isognomon has recently been recognized as the type of the genus; previously it was generally considered the type of another subgenus.  Either way, it tends to get illustrated as a noteworthy species, e.g. Springsteen and Leobrera.  A few regional books cover bivalves; for a likely Indo-Pacific form, the Bivalves of Australia set is among the best, but not everything ranges to Australia.  I do not know of a good reference that would review all possible species worldwide.  For example, there is one species name listed as the source for an Isognomon DNA sample that I could not find mentioned anywhere.  As a morphologically variable group, I suspect that there are some species that have been oversplit, but I. isognomon is the only one I know of offhand that has the very Malleus-like form.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa