Description of a new species of Unio

Shell elongated, rather compressed, very inaequilateral, the umbones laying at about one sixth of the whole length of the shell, rather smooth, with numerous fine concentric striae; umbones little prominent, decorticated in the adult, in half grown shells with conspicuous radiating folds, extending more or less over the disk of the shell; moreover a few radiating grooves occupy the anterior part of the shell, and microscopic radiating wrinkles of the epidermis cover the posterior slope; epidermis reddish-brown in the adult, yellowish olive-green in the young ones. Upper margin slightly curved, anterior margin rounded, slightly protruded below; ventral margin incurved, posterior margin forming with the upper one a more or less obtuse angle, regularly curved above, rounded below and running with a very obtuse angle at the umbonal ridge, which is rather obtuse, into the ventral margin. Ligament long, narrow, yellowish-brown. Nacre bluish white, more iridescent near the posterior part, brownish near the umbones; scarcely more than one short, thick, crenated tooth in each valve; a small knob in the left valve may perhaps be considered as a second tooth; lateral lamellae: 2 in the left valve, one in the right one; they are elongated, slightly curved, rather thick