ortmann: south American naiades. 



555 



The outline is "sulxiuadratc" according to Von Iliering. I should call it 

 rather subtrapezoidal or subrhomboidal, and this is due to the fact that the pos- 

 terior end is not much produced, and that the angle between the upper and the 

 posterior margins is somewhat prominent; consequently, the posterior slope is 

 not so much truncated as in other species, but a little elevated toward the ui)p(>r 

 posterior angle. On account of the shortness of the shell, the beaks are com- 

 paratively remote from the anterior end. 



Von Ihering has pointed out that there are variations in the beak-sculpture, 

 and I observe this also in my specimens. In most cases it is sharp, the bars are 

 narrow and distinct, and extend to the lower margin of the shell. But sometimes 

 the bars are more rounded, less distinct, and may not reach the lower margin. A 

 few finer radial bars are generally present upon the posterior slope. 



Measurements. 



Localitiea. 



Santarem 



Do 



Guapore 



Do 



Do 



Santarem 



7 



HupS, text-figure 



Height. 



Diameter. 



Beaks. 



16 1 



18 



20 



20.5 



24.5 



25 



27 



26 



. =86 pr. ct. of L. 

 =90 

 =83 



=85 

 = 88 

 = 86 

 = 90 

 = 76 



14 min 



17 



19 



18 



21 



22 



23 



23 



= 76 pr. cti. of L. 



= 85 



= 79 



= 75 



=75 



=76 



=77 



=68 



at 5.5 mm. =24 pr. ct. of L. 



6.5 

 6.5 

 6 



8 



8.5 

 10 



= 33 

 = 27 

 = 25 

 = 29 

 = 29 

 =33 



It should be remarked that Hupe's figure of the diameter (half shell) does 

 not agree with his measurements in the text. This figure would give a diameter 

 of only 18 mm. ( = 53 pr. ct.,) while the text gives 68 pr. ct. Both height and diam- 

 eter of Hupe's shell are less than in any of mine. Von Ihering gives the location of 

 the beaks at 39 to 41 i^r. ct. of the length, which is much greater than the figures 

 of Hupe (31 pr. ct. according to the figure) and of my shells. But I believe that this 

 discrepancy is due to a different way of measuring: I always measure parallel to 

 the ligament. 



Remarks. — My specimens certainly belong together; but I am not quite positive 

 that they might not be only the young stage of some other species {hanlcyana or 

 haro). The fact that some of mine are gravid does not demonstrate that they are' 

 adult or nearly adult, for we know that other Naiades become sexually mature, 

 when yet rather small. The further fact that those from Santarem were found 

 associated with baro and hanleyana indicates that they may belong to these species. 

 However, I am unable to decide this question. 



Anatomy. — Soft parts of two males and two gravid females (with glochidia) at 

 hand. The latter were found on July 20. Color of soft parts whitish. 



