1 146 rTVCriORHYXCHUS 



\"ar. mediastinum (Heude). 



Heude separates this from his Unio pftsteri on account of 

 its having more elevated beaks than that species. The type of 

 U. pfisteri, according to the figure, is so badly eroded in the 

 umbonal region that nothing of the beaks can be made out. 

 That of U. mcdiastinus is also somewhat eroded and its beaks 

 are not at all full. The posterior end of the type is a little 

 more blunt than the National Museum specimens or Heude's 

 figures of U. pfisteri. 



China. 

 Uuio mediastinus Heude. Conch. Fluv. Nank.. VIII, 1883, pi. 



T,xTi]. fig. 123. 

 Ptychorhynclms mediastinus Simpson, Syn., 1900, p. 851. 



Ptychorhynchus L.TiVis Haas. 



"Shell elongate-elliptical, subsolid, rather compressed, 

 rounded in front, bluntly pointed behind about the middle of 

 the height ; posterior ridge low, rounded ; angulate, basal 

 margin regularly curved. Beaks somewhat prominent, 

 situated at 29-100 of the total length; their sculpture 

 is invisible on account of erosion. Epidermis smooth, 

 shining, of a blackish-brown, with darker lines of 

 growth. Hinge consisting of two cardinals and vestiges of 

 two laterals in the left, one cardinal and vestiges of one lateral 

 in the right valve. Cardinals high, the one of the right valve 

 pyramidal, the anterior one of the left valve smaller and lower 

 than the posterior one, almost triangular. Laterals very short, 

 low, only indicated ; interval long, narrow and smooth. An- 

 terior cicatrices deep, rough, that of the anterior adductor and 

 that of the anterior retractor confluent. Posterior cicatrices 

 distinct, faint. Dorsal cicatrices united to a narrow groove 

 situated at the inner side of the interval. Beak-cavities shal- 

 low. Nacre reddish, bluish at the margin, not l)rilliant. 



Length 59, height 31, diam. 16 mm." (Haas). 



Type locality, Saghalin Island. 

 Ptychorhynchus hcvis Haas, Ann. Mag. Nat. Hist., (8). VL 



19T0, p. 498. 



