A new species of freshwater mussel in the genus Popenaias Frierson, 1927, from the Gulf coastal rivers of central Mexico (Bivalvia: Unionida: Unionidae) with comments on the genus Author Inoue, Kentaro Natural Resources Institute, Texas A & M University, College Station, Texas, USA & Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium, Chicago, IL, USA kinoue @ sheddquarium. org, https: // orcid. org / 0000 - 0001 - 6087 - 3290 Author Cummings, Kevin S. Illinois Natural History Survey, Prairie Research Institute, University of Illinois, Champaign, Illinois, USA, kscummin @ illinois. edu, Environmental Science Center, Laredo Community College, Laredo, Texas, USA, tmiller @ laredo. edu, Author Tiemann, Jeremy S. Illinois Natural History Survey, Prairie Research Institute, University of Illinois, Champaign, Illinois, USA, kscummin @ illinois. edu, Environmental Science Center, Laredo Community College, Laredo, Texas, USA, tmiller @ laredo. edu, & jtiemann @ illinois. edu, https: // orcid. org / 0000 - 0001 - 7635 - 1403 Author Miller, Thomas D. Author Johnson, Nathan A. Wetland and Aquatic Research Center, U. S. Geological Survey, Gainesville, Florida, USA Author Smith, Chase H. Biology Department, Baylor University, Waco, Texas, USA. Author Randklev, Charles R. Natural Resources Institute, Texas A & M University, College Station, Texas, USA & crandklev @ ag. tamu. edu, https: // orcid. org / 0000 - 0002 - 6755 - 1507 text Zootaxa 2020 2020-07-20 4816 4 457 490 journal article 10.11646/zootaxa.4816.4.3 1175-5326 3954602 7683A3B0-5833-49B6-A7CE-675D116DBC67 Popenaias berezai Inoue et al. n. sp. ( Figs 5 , 6 , 7 , 8A , 9A ) Common name: Mexico Hornshell FIGURE 4. Biplots from principal component analysis (PCA; A) and canonical variate analysis (CVA; B) of Fourier shape morphometrics. Colors and shapes of points correspond to species: blue circles, Popenaias popeii ; green squares, P. ganina ; orange diamonds, P. berezai n. sp. Polygons enclose convex hulls of each species. Outlined shell shapes represent a mean shape (top-right) and ±2 × SD on PC1 and PC2 axes. Type locality: Río Valles ( Gulf of Mexico—Río Pánuco—Río Tampaón ), Estación Micos , 20 km NW of Ciudad Valles , San Luis Potosí , Mexico , 22.11417 , -99.16166 . Type specimens: Holotype : CNMO 8037 (ex. INHS 90397.5 ) . Paratypes : from the type locality, CNMO 8038 (3) , FMNH 344800 (3) , INHS 90397 (9) , NHMUK 20191101 (3) , NRI 9603 (3) , UF 548816 (3) , USNM 1617023 (3) ; Ri ́o Claro ( Ri ́o Pánuco—Río Moctezuma—Río Amajac ), 5.5 km SE of Tamazunchale , San Luis Potosí , Mex- ico, 21.22150 , -98.75573 , INHS 90134 (3) ; Río Amajac ( Río Moctezuma ), 5.1 km SE of Tamazunchale , San Luis Potosí , Mexico , 21.22728 , -98.75437 , CNMO 8039 (2) , FMNH 344801 (2) , INHS 90152 (10) , NHMUK 20191102 (2) , NRI 9604 (2) , UF 548817 (2) , USNM 1617024 (2) ; Ri ́o Huichihuaya ́n ( Ri ́o Moctezuma ), Huichihuayán, Ejido Tazaquil, San Luis Potosí , Mexico , 21.47269 , -98.95768 , INHS 90167 (1) ; Ri ́o Tancuili ́n ( Río Moctezuma—Río Axtla ), Jalpilla , 5.5 km S of Axtla de Terrazas , San Luis Potosí , Mexico , 21.39008 , -98.87544 , CNMO 8040 (2) , FMNH 344802 (2) , INHS 90175 (9) , NHMUK 20191103 (2) , NRI 9605 (2) , UF 548818 (2) , USNM 1617025 (2) ; Río Tampaón ( Río Pánuco ), Álvaro Obregón ( Pujal ), at confluence of the ríos Valles and Tampaón, San Luis Potosí , Mexico , 21.84489 , -98.94373 , INHS 90183 (12) ; Ri ́o Huichihuaya ́n ( Ri ́o Moctezuma ), Rt. 120, 9 km WSW of Axtla de Terrazas , 12 km NNE of Xilitla , San Luis Potosí , Mexico , 21.43633 , -98.93345 , INHS 90192 (2) ; Río Amajac ( Río Moctezuma ), Temamatla , San Luis Potosí , Mexico , 21.23664 , -98.76189 , CNMO 8041 (5) , FMNH 344803 (5) , INHS 90199 (33) , NHMUK 20191103 (5) , NRI 9606 (5) , UF 548819 (5) , USNM 1617026 (5).