46 JOHN C. W. COPE
Fig. 3. Pie diagrams to illustrate the faunal composition and diversity of bivalve faunas in the Ordovician.
(a) Early Ordovician. Comparison between the numbers of species comprising faunas of the Llangynog Inlier.
Wales (Cope 1996b) and the near-polar Montagne Noire (Babin 1982a). Note the far greater abundance of
pteriomorphians in Wales, (b) Mid-Ordovician. Comparison between the numbers of species comprising the
faunas of high-latitude Spain (Babin & Gutierrez-Marco 1991), mid-latitude Avalonia (Cope 1999) and low-
latitude Australia (Pojeta & Gilbert-Tomlinson 1977). Note the increased importance of pteriomorphians at
low latitudes whilst the heteroconchs are much more diverse at median to high latitudes. (c) Late Ordovician.
Comparison of three low-latitude bivalve faunas to show faunal composition and generic diversity: Laurentia
(data summarized from various sources), Baltica (primarily after Isberg 1934) and Siberia (Krasilova 1970.
1979).