288 



POPULAR CONCHOLOGY. 



Paxyodon. Schum. (Hyria Lam.) — Shell equivalve, 

 obliquely triangular ; hinge 

 margin straight, both extremi- 

 ties elevated and winged; car- 

 dinal tooth long, and divided 

 into many parts, lateral tooth 

 long ; ligament external. Ani- 

 mal (according to Gray) has 

 the mantle lobe joined behind, 

 and two, short, double contrac- 



. . Paxyodon corrugata. 



tile siphons, like Iridina, but 



agreeing otherwise with Unio. — 2 species. 



Found in exotic lakes, covered with an olive-coloured 

 epidermis, and pearly within. 



Castalia. Lam. (Tetraplodon Spix.) — Shell equi- 

 valve, inequilateral, triangu- 

 lar, with the bosses eroded; 

 hinge with two laminar trans- 

 versely striated teeth, one is 

 posterior, distant from the 

 bosses, short and divided ; the 

 other anterior, long ; epider- 

 mis thick ; interior pearly. 

 Animal unknown. — 4 or 5 

 species. 



Lamarck says these shells 

 are intermediate between 

 Trigonia and Unio; they are found in the rivers of 

 Brazil, Paraguay, &c. &c. 



MoNOCONDYLiEA. D' Orb. — Shell equivalve, inequi- 

 lateral, subrotund, or angulated; hinge consisting of a 



