Original Description: Unio stevensii Lea, I. 1871. Description of three new species of exotic Unionidae. Proceedings of the Academy of Natural Sciences of Philadelphia 23:188.
Type Locality: “Yuruari River, tributary to Essequebo River, Guiana [=Venezuela]. R.P. Stevens.” (Lea, 1871:188).
Holotype: USNM 83901.
Paratypes: USNM 83901a. (2). ANSP 125550.
- Unio stevensii Lea, 1871
- Lea 1874a:22, pl. 7, fig. 19; 1874b:26, pl. 7, fig. 19.
Hyria stevensi (Lea, 1871)
- Simpson 1900:869; 1914:1216.
Hyria (Triquetrana) stevensi (Lea, 1871)
- Haas 1931:44.
Triplodon (Triquetrana) stevensii (Lea, 1871)
- Haas 1969:547.
Description of U. stevensii: “Shell double winged, very much folded, triangular, compressed, very inequilateral; valves somewhat thick, thicker before; beaks scarcely prominent; epidermis dark horn color, without rays; cardinal teeth small and sulcate; lateral teeth long, lamellar and somewhat curved; nacre white and iridescent.” (Lea, 1874: 22; pl. 7, fig. 19).
Shell compressed, with a feebly developed posterior wing, thickened in front; each valve with about three somewhat divergent pseudocardinals which are sometimes nearly smooth and others break into denticles; one granular lateral in the right valve and two in the left which are sometimes obliquely and faintly vertically striate; external sculpture much as in Hyria. Animal Unknown.” (Simpson 1900:869).
Range: According to Simpson (1900:869) found only in the Yuruari River, Guiana [=Venezuela].
Comments: One of two species of the Tribe Prisodontini found in Venezuela. This species can be separated from Paxyodon syrmatophorus by the presence of sculpture on the sides of the shell, and by the absence of anterior lateral teeth. This species groups with the other sculptured species in the genus Triplodon including; T. corrugata(Lamarck, 1819), Range: Eastern Peru to Guiana; south throughout Brazil (Simpson 1900), T. rugosissima (Sowerby, 1869) (Amazon River, [Brazil]), T. latialata (Sowerby, 1869) (Guiana), and T. transvera (Hupe, 1857) (Brazil). Simpson created the subgenusTriquetrana for this species in 1900 because of the lack of a well developed posterior wing and the presence of three somewhat divergent pseudocardinals. Not found in our expedition to the Yuruari River in 1994. Other Prisodontini in northern South America include: Prisodon (Prisodon) complanatus (Hupe, 1857) (Guiana) and Prisodon alatusSowerby, 1869 (Guiana).
Specimens Examined: USNM 83901. (Holotype). USNM 83901a. (2 Paratypes). Yuruari River a branch of the Orinoco [Essequibo] [Bolivar], Venezuela. R.P. Stevens. ANSP 125550.