ortmann: south American naiades. 499 



are at least 0.09 mm. lorio;. Tii one ,si)ccimen with iTumature slochidia no hook.s 

 could be seen. 



In this case also the breeding season fulls in the wiiitei- months of the northern 

 hemisphere, but apparently a little earlier than in the other species (end of No- 

 vember). 



Thus this species has anatomical characters of its own, chiefly observable in 

 the size and location of the marsupium. It agrees most closely with D. simillimus. 



3. Species from the drainage of the upper Parana. 



I have material belonging to the chile n.^is-group from the following tributaries 

 of the Parana: Rio Iguassii, Rio Tiete, and Rio Grande in Sao Paulo. A form from 

 the Iguassii is noticeably very closely related to the three species from the coastal 

 streams just described. We should bear in mind that the head-waters of the 

 Iguassu, from which this form comes, are in close jM'oximity to those of the Rio 

 Nhundiaquara and Rio Ribeira on the eastern watershed. 



11. DiPLODON decipiens Ortmann, sp. nov. 



Shells: PI. XXXVI, figs. 3, 4, 5, 6. Anatomy of gills: PI. XLV, fig. 4. Section of 

 gills: PI. XLVII, fig. 7. Glochidium: Text-fig. 4e, p. 409. 



Type-locality. — Creek, tributary to the Rio Iguassu, Serrinha, Parana, Brazil 

 (J. D. Haseman coll., December 23. 1908). Type-set: Carn. Mus. Cat. No. 

 61.9253, thirteen specimens, males, barren and gravid females, all with soft 

 parts. 



No Naiades have hitherto been known from the river-system of the Iguassu, 

 and, as in the preceding species, none of the names of species which may occur here, 

 can be ai^plied to om- specimens with any degree of certainty. Therefore we in- 

 troduce this form as a new species. 



In the shape of the shell this species is very close to the three preceding, es- 

 pecially imitator and simillimus, which it resembles in its subelliptical or sub- 

 trapezoidal outline. The latter shape is seen chiefly in younger specimens, while 

 older ones become more subelliptical. The posterior ridge and the posterior end 

 are never biangulate as in vicarius. In the gloss.y epidermis, D. decipiens also 

 agrees better with imitator and simillimus, and the radial lines formed of fine 

 wrinkles are poorly developed. The general description given for imitator might 

 be repeated for this species, and the beak-sculpture in particular has the same 

 character. Nevertheless the following [X'culiarities should be mentioned as 

 diagnostic: 



