Harpidium , a New Pentameroid Brachiopod Genus from Southeastern
نویسنده
چکیده
In an earlier paper^ I described the new genus Brooksma from a series of sediments in southeastern Alaska tentatively referred to the upper Silurian. In that paper will be found a brief discussion of the faunal affinities of the series. A more detailed study of the Brooksina fauna together with the famias of lower and liighei horizons strengthens the belief that the formations in question should be assigned to the upper Silurian rather than to the lower Devonian. There are certain elements suggestive of the Devonian, but there is little to compel a correlation with the widespread and characteristic lower Devonian or Helderbergian faunas. On tlie other hand, our scant laiowledge of latest Silurian normal marine sediments v»'ith their contained faunas leaves a faunal gap into which these Alaskan faunas may well fit. Within this time interval should be placed, I think, those faunas of the Ural Mountains commonly referred to the lower Devonian. In the limestone series characterized by Brooksina alaskensis is another pentameroid of considerable interest. To this genus the name Harpidtum is here given. The genus is not represented elsewhere than in this restricted zone of the upper Silurian of Southeastern Alaska, so far as IniOAvn. Conchidium {?) occidentalis Hall from the Guelph dolomites of Ontario resembles Harpidium in general form. Detailed knowledge of the structure of the species is wanting. G. (.<^) occidentalis has, however, obscure radial plications that are wanting in the Alaskan species of Harpidium. Even so its affinities may prove to be closer to Ilarpidiuin than to Conchidium. to which it was doubtfully referred by Hall and Clarke.
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