1895. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



383 



Fig.l. 



UNIO SUBPLANATUS, NEW SPECIES. 



diameter, 25 mm. 



The theory advanced by W. Amalsky,i that the Naiades descended 

 from the Anthracosida?, seems the more reasonable one, as the two fami- 

 nes agree in many essential i)oints of shell structure, and the latter 

 were probably inhabitants of the 

 fresh waters of the Carboniferous 

 and Permian periods. 



UNIO SUBPLANATUS, new spe- 

 cies. 



Shell rather large, somewhat 

 triangular and compressed; 

 growth lines strong and elevated ; 

 dorsal region and posterior slope 

 rounded ; beaks not very promi- 

 nent; area of the lateral teeth 

 strongly curved; cardinals 

 rather wide, parallel, separated intemau.ew, 



by a narrow socket. Length, 85 mm. ; height, 57 mm. 

 Locality. — Duck Creek, Dickens County, Texas. 



Of this line species only a single cast of a right valve of ferruginous 



clay conglomerate, and what is 

 probably a right valve of the 

 same, badly incrusted and buried 

 in a limestone matrix, were 

 received. The latter, on being 

 carefully cleaned, shows the shell 

 to have been of moderate thick- 

 ness, and to have the curious, par- 

 allel, cardinal teeth that charac- 

 terize most of the Unios of the 

 southern hemisphere to-day. The 

 lateral teeth are shown plainly at 

 their posterior end, but the hinge 

 plate is so worn away and in- 

 jured that they are not visible along the rest of it. 



UNIO DUMBLEI, new species. 



Shell elongated oval, widest at the region of the beaks, rounded before 

 and behind; anterior end very short; posterior and anterior slopes ele- 

 vated and almost ridgelike, with a flattened or slightly excavated area 

 in the middle of the disc; dorsal margin rounded; base of the shell 

 nearly straight or sometimes a little emarginate; beaks rather promi- 

 nent; ligament small, but elongated; growth lines ratlier strong. 

 Length, 55 mm.; height, 25 mm. ; diameter, 18 mm. 



Fig. 2. 



UNIO SUBPLANATUS, NEW SPECIES. 



Cast from outskle of right valve. 



'Paleoutographica, XXXIX, p. 198, Stuttgart,1892. 



