ortmann: south American naiades. 495 



n. DiPLODON SIMILLIMUS Ortmaiin, sp. nov. 



Shells: PI. XXXV, fi^s. li, 4, 5, G. Anatomy of ijilU: PI. XLV, fig. 2. 

 Glorln'diiiiii: Text-fig. 4c, p. 4()9. 



Type-locality.— Rio Nhuiidiiuiuara, Morretes, Parana, Brazil (J. D. Ha.seman 

 coll., January 3, 1909). Type-set: Carn. Mus. Cat., No. 61.9250. Thirty-two 

 specimens with soft jiarts, males, barren and gravid females with gloeliidia. 



About a dozen additional specimens belonging to the same original lot have 

 been studied. The locality is in a small coastal stream emptying into the Bay of 

 Paranagua. 



No shells have ever been reported from the region of Paranagua Bay in Parana. 

 However, from a little less than one hundred miles to the south, in Santa Catharina, 

 near Barra Itapocu (I believe that the Rio Itapoca, as given by Marshall, stands for 

 this), Diplodon santamaruE Simpson has been described (Simpson, 1914, p. 1270; 

 and Marshall, 1917, p. 386, PI. 52, fig. 6; PL 55, figs 1-4). This is founded upon 

 three specimens only, and resembles our sjiecies to a degree. But judging from 

 description and figures, it is somewhat larger (max. 63 mm.), longer (H. 52-59 

 pr. ct. of L.), and the hinge has the posterior tooth of the left valve missing. Since 

 nothing is known of the anatomy of D. santamarice, and the locality is not the same, 

 it would be rash to unite our specimens with this species. 



Our species also is much like U. martensi Von Ihering, and might fall under 

 this according to Von Ihering's conception. But it cannot be united with it on 

 account of the different dimensions. While in martensi the height is said to be 

 from 49 to 57 pr. ct., our specimens are mostly less elongated, with the height from 

 53 to 66 pr. ct. of the length. In D. martensi the diameter is 32 to 35 pr. ct., in the 

 present species from 26 to 37 pr. ct. (this agreeing better with martensi than with 

 imitator). But in the absence of exact localities for martensi and any knowledge 

 of its anatomy, and in view of the general resemblance of all of these shells, it is 

 impossible to identify our shell with any previously described, and no other alterna- 

 tive exists, except to describe it as new. 



In the characters of the shell D. simillimus is very close to D. imitator. The 

 description of the latter species would fit it very well, and I shall here only emphasize 

 the distinguishing characters. 



1. D. simillimus is a smaller shell (max. length 61 mm., as against 80 mm. in 

 imitator-) . 



2. The trapezoidal shape, with an angle between the upper and the posterior 

 margins, is seen here only in very young shells. In older shells these two margins 

 form a rather regular curve. 



