6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 82 



Genus ANODONTITES (?) Bruguiere 



U.S.N.M. No, 372845 includes a number of casts from Bib- 

 lian that evidently were made in pearly fresh-water mussel shells. 

 A few of them show remains of the shell on the surface. These 

 fragments seem to have had a rather thick prismatic layer, which 

 leads to the belief that the species belongs to the genus Anodontites, 

 as a thick prismatic layer is one of the features of that genus. In 

 most of the specimens one valve has slipped toward the ventral 

 margin so that its beak is beneath the beak of the other valve. This 

 slipping likewise may indicate the genus Anodontites^ which has no 

 teeth of any kind to serve to hold the two valves in place. The 

 hinges of other fresh-water mussels of the region have pseudocardinal 

 and lateral teeth, the former serving to direct the valves when the 

 shell is closing and both helping to hold the valves in position when 

 closed. As the teeth in one valve interlock with those of the other, 

 force enough to break the teeth is necessary to make the valves slip. 



NOTE ON DISTRIBUTION OF RECENT NAIADES 



The great majority of recent South American naiades are found in 

 the Atlantic drainage. On the Pacific side of the Andes almost 

 none occur north of Chile. Diplodon atratus (Sowerby) ^ has been 

 reported from Peru. Castalia crosseana Hidalgo ^ and Diplodon 

 paei (Hidalgo) ^ were described as coming from the Province of 

 Imbabura, Ecuador, which lies almost wholly in the Pacific drainage, 

 although it seems probable that some small streams in its eastern 

 part may drain into the Atlantic. Castalia crosseana is unrelated to 

 any form found in the Pacific drainage, and it is of interest that its 

 nearest relative is Castalia linki (Marshall) *^ of the Eiver Sinu, 

 Colombia, Caribbean drainage. Diplodon pazi has no relative in the 

 Pacific drainage, but many in the Atlantic. 



The beak sculpture of all naiades on the Pacific side of the Andes 

 is much reduced, consisting of a few radial bars, which occupy a 

 small area at the beaks. The sculpture of many genera and species 

 in the Atlantic drainage is bold, often occupying a large area. In 

 some specimens of Hyrla rugosissima Sowerb}^, a large species, the 

 sculpture covers nearly the whole shell. 



* Unio atratus Sowerby, 1839. Conchological manual, fig. 148. 



* Castalia crosseana Hidalgo, 1865. Journ. Conchyl., p. 316, pi. 14, fig. 2. 

 s Castalia pazi Hidalgo, 1868. Journ. Conchyl., p. 353, pi. 13, fig. 6. 



« Tetraploilon linki Marshall, 1926. Proc. U. S. Nat. Mas., vol. 69, art. 12, p. 6, pi. 1^ 

 figs. 6, 7 ; pi. 3, fig. 2. 



