ortmann: south American naiades. 



489 



This specie.s has [bv indifferont and uiu-haractorLstic outHiic of the forms of 

 the chilensis-gvoup: subclhptical or subtrapezoidal, with upper and lower margins 

 subparallel, and rather elongated and compressed shell. It is, however, remarkable 

 for the anterior location of the beaks (18 or 19 pr. ct. of the length). There is no 

 radial furrow or groove on the posterior slope. 



The color of the epidermis of my specimen (the largest known) is dark brown, 

 and the epidermis is wrinkled with concentric lamelhe, l)ut it has l)een largely 

 eroded. According to Von Ihering, the color is dark brown in the larger specimens, 

 but dark olive in smaller ones, sometimes with lighter green in i)laccs. The color 

 of huapoisis is brown posteriorly, grading to wax-yellow anteriorly. 



In all other respects, chiefly in the hinge-teeth, my specimen agrees with the 

 description of frenzeU; only the posterior end of the shell is a little more broadly 

 rounded, but not very different from the specimen figured by Von Ihering on plate 

 4, fig. 12/. 



D. huapensis has been compared by Bartsch with frenzeli, and he says that it 

 can readily be distinguished from it by the narrower outline, that means to say by 

 the height being less in proportion. This, however, is not correct, as can be seen 

 by comparing the measurements. 



The only difference I can see hi huapensis is the more tapering posterior end. 

 But since this species is founded upon two specimens, of which only one has been 

 figured, this miglit very well be an individual character. 



In the following measurements I leave out Von Ihering's specimens from Chile, 

 which appear to me a little doubtful. 



Thus my specimen is more compressed than any of the others; however, a 

 variation of the diameter from 23 to 29 pr. ct. is not at all unusual. 



Aiiatomi/.—Tht' specimen at hand has been preserved with the soft parts, and 

 proved to be a gravid female with glochidia. 



Color of soft parts whitish, with black pigment near anal and branchial open- 

 ings extending forward a good distance along the margin of the mantle, and be- 

 coming brown. 



