1 198 TETRAPI.OnON 



It is clear, therefore, that we are deahng with two related 

 species, which, however, differ in the characters of the hinge, 

 the position of the beaks, etc. 



The free border of tlie lunula on the Junia specimen is 

 slightly convex, which is similar in T. amhiguus. 



Length 46, height 30. diam. 21 mm. The beaks are situated 

 at 37-100 of the length." (von Ihering). 



Type locality. Rio Jurua, Brazil. 

 Tctraplodon ambigiiiis von Ihering, Rev. Mus. Paul., ^T, 



1904, p. 460. 

 Tctraplodon junianiis von Ihering. Abhandl. Senckenb. 



Naturf. Ges., 32, ic)io, p. 126. 



Tetraplodon daro von Ihering. 



"This rather thick-shelled species with high, inflated beaks, 

 straight basal margin and long oval form has absolutely no 

 near relationship to the genuine Castalia ambigua of Lamarck. 

 The beaks are placed far forward, situated at 16-100 of the 

 length. I have it from the Amazon." (von Ihering). 

 Unio amhiguus Kuster. Conch. Cab., 1851, p. 165, pi. XLVin, 



fig- I- 

 Castalia ambigua SowErbv, Conch. Icon., XVII, 1869, pi. i, 



fig. ifl-r. 



Tetraplodon anibii^uus, (part), Simpson, Syn., 1900, p. 863. 

 Tetraplodon baro von Ihering, Abhandl. Senckenb. Naturf. 

 Ges., 32, 1910, p. 127. 



Tetraplodon quadrilaterus (d'Orbigny). 



Shell rather large, triangular rhomboid, subsolid, inflated, 

 inequilateral ; beaks high and full, with very strong, wide, 

 radial ribs, which extend almost to the base ; posterior ridge 

 very high, sharply angled, ending in a blunt point near the 

 base of the shell ; anterior end narrow and rounded ; base 

 lightly curved; posterior end sharply and obliquely truncate, 

 raised to an angle behind the short ligament ; dorsal slope 

 racHally sculptured near the beaks ; epidermis brownish, thick, 

 dull, showing growth lines; pseudocardinals subcompressed, 

 split, vertically striate ; laterals single in the right valve, double 



