I068 PHVSUNIO 



or high, their sculpture consisting" of corrugated, zigzag-radial 

 bars ; posterior ridge low, ending below the median line on 

 adult shells, in a feeble point ; surface with fine, concentric 

 growth lines, plicalely sculptured on the dorsal slope; epider- 

 mis greenish-yellow, marked with imperfect bands and rays of 

 bkie-green, subshining ; nacre bluish, somewhat iridescent ; 

 teeth delicate, lamellar, laterals two in the right valve and 

 three in the left. 



Length 65, height to point of wing 50, diam. 17 mm. 



Siam ; Cambodia. 

 Unio eximms Lea, Pr. Ac. N. Sci Phila., VIL 1856, p. 93; 



Obs., VI, 1857, p. 14, pi. XXV, fig. 8 ; Jl. Ac. N. Sci. Phila., 



IIL 1858, p. 294, pi. XXV, fig. 8. — SowERBY, Conch. Icon., 



XVI, 1868, pi. LXXXIX, fig. 481. 

 Mar gar on (Unio) eximius Lea, Syn., 1870, p. 28. 

 Physunio exhnins Simpson, Syn.. 1900, p. 831. — Haas, Conch. 



Cab., Unio, 1912, pi. 34. figs. 6-8. 

 Unio semiquadrata SowERnv, Conch. Icon., XVI, 1866, pi. 



xi.virr, fig. 258. 

 Unio semiqnadratus P.ETel, Conch. Sam., Ill, 1890, p. 167. 



The old shells of this species are decidedly triangular, hav- 

 ing a high post-dorsal wing, and have almost exactly the ap- 

 pearance of a Hyriopsis. P)Ut the younger shells are rather 

 more inflated in proportion and show relationships to P. grav- 

 idas and snperbiis. Their beak sculpture is decidedly zigzag- 

 radial and not concentric as it is, in all cases where I have been 

 able to examine it. in Hyriopsis. 



Physunio Friersoni n. n. 



Shell obovate or subtriangailar. thin, rather compressed, pale 

 green, neither radiated or sculptured ; beaks small, pointed ; 

 posterior ridge scarcely developed ; anterior end much nar- 

 rowed, rounded, angled above; base line nearly straight, full 

 near the posterior end ; dorsal line with a high posterior wing, 

 which is almost squarely truncate behind ; posterior end widely 

 and evenly rounded ; lunule excavated ; pseudocardinals large, 

 lamellar. 



Assam. 



