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 both genera are similar in many ways, casts of both genera 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 re-assigned to Liopistha (Sergipemya) alta (Roemer). Pleuromya henselli (Hill) is re-assigned 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. Two sets of species are distinct morphotypes: a smaller-sized set of H. knowltoni, H. tarrantensis, H. tlahualiloensis, H. kellumi, and a larger-sized set of H. cymbiformis, H. austinensis, H. vulgaris, H. budaensis, and H. auroraensis. 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. These infaunal suspension feeders occupied calcareous mud and carbonate shelf substrates.