Abstract

Species of the megaorder Poromyata, although common and relatively diverse in Albian–lower Cenomanian Comanchean strata in Texas and northern Mexico, have been neglected as biostratigraphic markers and paleoecological indicators. Since 1852, more than a dozen species have been identified as Homomya Agassiz, order Pholadomyida, superfamily Pholadomyoidea or Pleuromya Agassiz, order Pholadida, superfamily Pleuromyoidea. Because valve morphologies of the two genera are similar in many ways, casts are difficult to separate. Statistical analysis of key morphological properties objectively defines species concepts and assesses synonymies. Eight species are retained in Homomya; four are synonymized with these. Two species are provisionally retained in “Homomya” although they differ significantly. One species is reassigned to Liopistha (Sergipemya) alta (Roemer, 1852). Pleuromya henselli (Hill, 1893) is reassigned to Panopea.

Homomyid species range from upper Aptian to lower Cenomanian of the Comanchean Series in Texas and Mexico. Their ranges vary in duration from one million years up to eight million years. These infaunal suspension feeders occupied calcareous mud and carbonate shelf substrates. Two sets of species are distinct morphotypes: a smaller-sized set of H. knowltoni Hill, 1895; H. tarrantensis Perkins, 1961; H. tlahualiloensis Perkins, 1961; and H. kellumi Perkins, 1961 and a larger-sized set of H. cymbiformis Perkins, 1961; H. austinensis Shattuck, 1903; H. vulgaris Shattuck, 1903; H. budaensis Whitney, 1911; and H. auroraensis Perkins, 1961. Two end-member morphotypes are represented by the “streamlined” Homomya knowltoni, which is an elongate, slightly inflated form with a relatively high umbo, and the cylindrical Homomya budaensis, which is a very elongate, tubular, inflated form with a very low umbo.

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