ortmann: south American naiades. 497 



10. DiPLODON viCARius Ortmann, sj). nov. 



Shells: PI. XXXV, fig8. 7, S; PI. XXXVI, figs. 1. 2. Anakmy of uills: PI. XLV, 



fig. 3. ainchhlium: Text-fig. U, p. 469. 



Type-locality. — In crocks, Aqua Qucnte (eight miles from Iporanga), Sao 

 Paulo, Brazil, tributaries of Rio Ribeira (J. D. Hascman coll., November 27, 1908). 

 Type-set: Carn. Mus., Cat. No. 61.92.51; fifteen s])ecimens all with soft parts, 

 males, barren and gravid females. 



Additional Locality. — Rio Ribeira, Iporanga, Sao Paulo, Brazil (J. D. Haseman 

 coll., December 1. 1908). One specimen, male, with soft parts. 



Only one species of Diplodon has been described from the Rio Ribeira; this is 

 D. mimus Simpson (1914, p. 1249; Marshall, 1917, p. 383, PL 51, fig. 3) from Iguape, 

 Sao Paulo, at the mouth of the river. As has been pointed out above (p. 486), 

 this species might possibly be D. granosus. But on the other hand a few particulars 

 agree with the present species, as, for instance, the biangulation of the posterior 

 end and the general resemblance to Elliptio complanatus mentioned by Simpson. 

 Yet our shells cannot be this, because they are larger, less convex, and have dif- 

 ferent dimensions. D. mimus is smaller (max. 45 mm.), and has, according to 

 the measurements given, a considerably higher (60 to 76 pr. ct.) and more swollen 

 (D. 33 to 46 pr. ct.) shell, while D. vicarius has the height only from 52 to 63 pr. ct. 

 and the diameter from 26 to 31 i^r. ct., and is a good deal larger (L. 53 to 68 mm.). 

 Of course, our form may fall under martensi Von Ihering, but for the same reasons 

 as in the case of the two preceding species, it cannot be called by this name, and 

 thus we must describe it as new. 



It may perhaps be that D. vicarius, of w^hich we do not know the beak-sculp- 

 ture, is the older stage of the young si)ecimens recorded from Iporanga as D. 

 granosus (See p. 485). The shape and dimensions agree fairly well, but the size 

 is very different, the maximum length of granosus being only 29 mm. and no inter- 

 mediate specimens between these and minimum length of vicarius (53 mm.) are 

 at hand. Thus the question must remain unsettled. D. granosus from other 

 localities is also always much smaller than vicarius. 



This species is also extremely similar to D. imitator and D. simillimus. In size 

 it stands between them (max. length 68 mm.). The outline is also sub trapezoidal 

 or subelliptical, and the shell is quite compressed, resembling the shape of Elliptio 

 complanatus of the United States. The lower margin in the shells before me is 

 always rather straight, but I have not very young si)ecimens. However, from the 

 growth-lines it is seen that young shells must have had a gently curved lower margin. 

 In none of my specimens is the beak-sculpture preserved. 



