NO. nil. PROCEEDINGS OF THE NATIONAL MUSEUM. 371 



shows tbe surface, especially near the beaks, to be covered with slight 

 pustules, which ill the types are worn, and the valves have the radiating 

 wrinkles on the posterior slope common to the species of the Asperri- 

 7)1 us gvou\). 



Dr. Mearns ])rocuied a single right valve of what 1 believe is the 

 young of this species. It is in a better state of preservation than Lea's 

 si)ecimens, and exhibits quite distinct, scattered tubercles. 



UNIO UNDULATUS, Barnes. 



Unio itndulaiHS, Barnes, Am. Jourii. of Science, VI, p. 120, pi. ii, fig. 2. 

 Unio laticosiaiii-s, Lea, Trans. Am. Phil. Soc, X, pi. i, &g. 2; Obs. on the Genus 

 Unio, IV, p. 42, pi. i, fig. 2. 



A single, badly broken, and much worn right valve of what is no 

 doubt this species was obtained in Kinney County, Texas. Unio lati- 

 costatus, though sometimes more delicately and evenly jDlicate than 

 Unio tmdulatus, is undoubtedly a mere variation of Barnes' species. 



UNIO POPEI, Lea. 



Unio popei, Lea, Jouru. Acad. Nat. Sci., lY, p.372; Obs. on the Genus Unio, VIII, 

 p. 54. 



The types of this species came from Devils Eiver, Texas, and the 

 Eio Salado, New Leon, Mexico. Since the time of publication it has 

 been rediscovered in both the typical localities by the Biological 

 Expedition of the United States Department of Agriculture. Dr. 

 Mearns obtained numerous valves in tolerably fair condition from Kin- 

 ney County, Texas. 



This, with Unio i)oeyanus^ Lea, a closely allied form from ^Mexico, 

 forms a small group which does not seem to be very closely related to 

 the Unione fauna of Texas, but rather belongs to that of Mexico and 

 Central America; aud the two species are evidently closely allied in 

 their somewhat sulcate sculpture and delicate, soft, lurid nacre, to the 

 groui) typified by Unio rotceUi of Lake Nicaragua. 



UNIO MITCHELLI, Simpson. 



(Plate XXXII, figs. 1-3.) 



Unio mitchelli, Simpson, Proc. U. S. Nat. Mus., XVIII, p. 5, 1895. 



Shell rhomboid-oval, solid, rather inflated, rounded before, somewhat 

 biangulate behind; dorsal margin curved; base slightly rounded or 

 straight, or sometimes a little emargiuate; growth lines strong, irregu- 

 lar anteriorly; ligament rather large and prominent; ei)idermis coarse, 

 often shining, varying from light yellowish brown to black; beaks fairly 

 prominent, showing slight traces of concentric aud rather strong, cor- 

 rugated sculi)ture; cardinal teeth rather strong, short, and stumpy, 

 slightly ragged; laterals short, heavy, and club-shaped, covered with 

 granular sculpture which has a tendency in very solid shells to become 



