A NEW GENUS AND TWO NEW SPECIES OF SOUTH 

 AMERICAN FRESH-WATER MUSSELS 



By William B. Marshall 



Assistant Curator, Division of Mollusks, United States National Museum 



The new genus here described affords a resting place for the unique 

 species described by Higgins as Mycetopus falcatus and which, in the 

 past has been shifted from the genus Mycetopoda (Mycetopus) of the 

 family Mutelidae to the genus Solenaia of the family Unionidae, and 

 back to Mycetopoda. 



The new species of Anodoniiies and Mycetopoda were collected by 

 Dr. Henry Pittier, of Caracas, Venezuela, whose donations from time 

 to time have enriched the collection of the United States National 

 Museum with material collected in that country. 



MYCETOPODELLA, new genus 



Shell very elongate, falcate, wide at the rear, much narrower in 

 front where each valve has a radial swelling and abruptly descends. 

 A marked, broad, radial constriction from the beaks to the ventral 

 margin. Beaks very near the anterior end. Hinge line without 

 teeth, nearly straight behind the beaks, just in front of the beaks it 

 is slightly excavated and has a decided hmule. It then abruptly 

 merges into the anterior margin. Ligament very long. Sinulus 

 long, narrow, forming a very acute triangle. Posterior ridge sharp; 

 anterior ridge much more pronounced. Posterior area roughened by 

 numerous, nearly perpendicular growth hnes and slight lamellations 

 of periostracum. Anterior area rougher with many sharply curving, 

 deeply impressed growth Hnes. Ventral area nearly smooth and 

 slightly glossy, but with moderate growth lines which run horizon- 

 tally. Periostracum dull, with numerous microscopic radiating striae 

 like those usually found in the Mutelidae. These lines number about 

 90 per millimeter. Anterior adductor scar pyriform, rather deep, 

 placed far forward. Posterior adductor scar scarcely visible. Sev- 

 eral minor but well-marked muscle scars just behind the anterior 

 adductor scar. 



The above generic name is proposed for the single species now 

 known, described by Higgins as Mycetopus falcatus. This shell can 

 not be placed in the genus Solenaia, and in many characters it differs 

 so widely from Mycetopoda, as shown below, that it should not be 

 included in that genus. 



No. 2678.-PROCEEDINGS U. S. NATIONAL MUSEUM. VOL. 7I,ABT. 6 

 2894&-27 1 



