476 



MEMOIRS OF THE CARNEGIE MUSEUM. 



Remarks: The chief characters of this species, so far as I am able to make 

 them out from the figure and description, and the single specimen at hand, by 

 which it differs from the other species of this group, are found in the general shape 

 (moderately elongated, slightly wider behind, with rounded posterior angle), 

 the beak-sculpture, which covers a rather large portion of the disk, and the rough 

 character of the posterior slope. The greater compression of our shell probably 

 is individual, and also the emargination of the posterior margin. 



2. DiPLODON GUARANIANUS (D'Orbigny). 



Unio guaraniana D'Orbigny, 1835, p. 37; 1843, p. 608, pi. 69, figs. 10-12. 



Type-locality. — Rio Parana, Itaty, Province of Corrientes, Argentina. No 

 other locality previously known. 



New Localities. — Paraguay River, Corumba, Matto Grosso, Brazil (H. H. 

 Smith coll. ) . One specimen, j uv. In swamps of Lamliare, near R. Paraguay, Asun- 

 cion, Paraguay (J. D. Hascman coll. March 31. 1909). One complete specimen, 

 6 left valves. Rio Paraguay, Sao Luis de Caceres, Matto Grosso, Brazil (J. D. 

 Haseman coll. May 25, 1909). One male, with soft parts, and seven specimens, 

 shells only. 



Distribution. — Middle Parana above the junction with the Paraguay River in 

 Argentina and Paraguay, and Paraguay River through Paraguay as far as Matto 

 Grosso, Brazil. 



I disagree with previous authors, and regard this species as being distinct from 

 D. hyhvus. My specimens answer very well to the description and figures of 

 D'Orbigny, and they differ from hylcvus in their somewhat smaller size, in the more 

 distinctly truncated (more steeply descending) posterior margin, forming a more 

 distinct lower posterior angle, but chiefly in the beak-sculpture, which consists 

 of a smaller number of bars, which are heavier, chiefly posteriorly, and arc not so 

 rugose. My specimens are also more swollen than the single individual of hyloeus 

 at hand, but the latter is, as has been stated, probably exceptional in this. 



The beak-sculpture is somewhat variable, chiefly in the length of the bars, 

 which are from 15 to 20 mm. long, and generaUy cover more than half of the disk, 

 but in the larger shells, sometimes less. There are twelve to fourteen radial bars, 



