NEW AND LITTLE-KNOWN SPECIES OF SOUTH A^fERICAN 

 FRESH-WATER MUSSELS OF THE GENUS DIPLODON. 



By William B. Marshall, 



A$nttant Curator, Division of Marine Invertebrates, United States National Museum. 



The new Diplodon herein described under the name felipponei was 

 received in 1915 from Dr. Florentine Felippono, of Montevideo, 

 Uruguay. The one described under the numeforiis was received from 

 the same donor about three years ago and has been in the collection 

 of the United States National Museum under the name of 

 D. delodontus. 



Illustrations are given of six other species of Diplodon described by 

 Mr. C. T. Simpson from material in the collection of the United 

 States National Museum. Hitherto these species have not been 

 figured. 



DIPLODON FELIPPONEI, new species. 



Plato 50, figs. 1-3; plate 51, fig. 1. 



Shell thick, heavy and moderately swollen, elliptic in outline, valves 

 greatly thickened in front. Gaping slightly front and back. Surface 

 nearly evenly rounded and lacking a clearly defined posterior ridge. 

 Anterior atui posterior portions rounding up gently into the middle 

 portion of the shell. Middle of the posterior area with a low, rounded, 

 radial rib, other parts of shell obscurely radiately striated. On the 

 middle portion the striae become more pronounced and partake of 

 the nature of obsolete ribs. Rest periods about seven, indicated by 

 a concentric elevating of the surface above the succeeding growth. 

 Color light yellowish chestnut at the beaks, deepening regularly 

 toward the margins, where it becomes dark chestnut. Periostracum 

 shining, paper-like, tending to peel and curl at the posterior margin. 

 Nacre silvery white, slightly iridescent at the posterior end, obsoletely 

 thimble-pitted or granular. Anterior adductor scar deep, especially 

 at its upper part, posterior adductor scar nearly superficial. Other 

 muscle scars deeply punched. Pseudocardinal teeth large and heavy 

 and much split up. Right valve with a largo lateral tooth which is 

 granular on both its surfaces. Left valve with two lateral teeth 

 which are granular on their inner faces. Sinulus long, narrow, 

 slightly bowed and ending in a sharp point. 



Proceedings U. s. National Museum. Vol. 53-2209. 



381 



