ORTMANN: south A^rERICAN NAIADES. 621 



consisting of radial bands of short, subconcentric wrinkles. These stripes may 

 also be seen upon the posterior section of the shell, but less frequently and less 

 distinctly'. 



Measurements. 



Simpson's measurements are: Length 61 mm.; Height 39 mm. = 64 pr. ct. of L. ; 

 Diameter 22 mm. = 36 pr. ct. of Length. 



Remarks. — The original description and that given by Simpson are scarcely 

 sufficient to enable the species to be recognized, but none of the characters given 

 conflict with those exhibited by my specimens, and the measurements apply very 

 well. Since the original .4. iheringi comes also from the same river-system (Guahj^- 

 ba) as- my specimens, I have no doubt that we are dealing with this species. 



Anatoviij. — Two males, and one female are at hand for study. 



The soft parts are absolutely identical with those of A. patagonica. 



6. Group of Anodontites trapesialis. 



Shell strongly oblique, subovate to subtrapezoidal, narrowly rounded, or 

 bluntly pointed behind. Epidermis shining, only here and there, and not always, 

 with scalariform radial bands of wrinkles. Prismatic border narrow and of equal 

 width. 



A rather well defined group, distinguished also by the large and comparatively 

 thin shell: the largest species of the genus belong here. ITsually we discover that 

 the valves are gaping anteriorly, and sometimes also posteriorly. Whether this 

 is connected with the anatomical structure, or with habits, is not kno\vn. There 

 is hardly a question that the genus Leila is descended from forms belonging to this 

 group. s 



Von Ihering has given a partial key to the species (1890, p. 157), which I 

 have used to great advantage. But great difficulties arise in distinguishing the 

 species, and young individuals are often very hard to correlate with older ones. 

 Although I possess good material representing this group, it includes only com- 

 paratively few forms, so that I am unable to form a definite opinion as to those which 

 arc not represented. I treat my siiecimens here under the names to which they 

 seem to belong, without going into detail as to their aflanities and relationships. 



