ortmann: south American naiades. 591 



posterior section of the sliell. Anteriorly there arc sliort, concentric wrinkles, 

 arranged in scalariform, radial bands. Posteriorly the wrinkles are rather irregu- 

 larly radial, assuming generally an oblique direction, forming radial bands of 

 loops or V-shaped festoons, often anastomosing, and more or less reticular ("like 

 dried paint")- In the middle of the shell the two types of sculpture pass into each 

 other: the short, subconcentric, scalariform wrinkles become rather suddenlj' V- 

 shaped, and assume the oblique or radial direction. On the posterior slope and 

 near the lower margin, the wrinkled sculpture is more or less obscured by sub- 

 lamellar concentric striie. Color of epidermis, in very young specimens, yellowish; 

 later it becomes brownish olive or dark greenish to blackish, generally more brown- 

 ish toward the beaks, and more blackish toward the margins. Sometimes (in 

 strong transmitted light) there ar(> dark color rays upon the posterior slope. 



Hinge-line nearly straight or gently convex posteriorly, descending anteriorly, 

 a little irregular just in front of the beaks. Ligamental sinus moderate, triangular, 

 wider than deep, its anterior margin slightly oblique to the hinge-line. Nacre 

 blueish white, grayish white, lurid, often showing brownish or greenish discoloration. 

 Prismatic border rather narrow, subequal in width, of grayish color. 



Cavity of shell and l^eaks shallow. Anterior adductor-scar well marked, im- 

 pressed, irregularly elliptical. Anterior retractor-scar only partially separated 

 from adductor-scar, connected with it narrowly or more broadly, and very variable 

 in this respect. Anterior protractor-scar separated from adductor-scar. Pos- 

 terior adductor-scar less impressed, rounded or subovate, posterior retractor- 

 scar forming an upper process of it. Dorsal scars generally absent, but in a few 

 cases there is an indistinct single one. Pallial line distinct, simple, subparallel 



to the margin. 



Measurements. 



Remarks. — I have no doubt that my specimens represent A. crispata. Thej' 

 agree fairlj^ well with Sowerby's figure of Anodon reticulatus, and very well with 

 Simpson's description. But there are several closely allied, if not identical, species, 

 chiefly A. napoensis Lea (Obs. XII, 1869, PI. 53, fig. 137, and Germain, 1910, p. 

 C 64, PL 2, figs. 3, 4) from Rio Najio (tril)utary to the upper Amazon in Ecuador) 

 and Rio Unuyacu (tributary to Napo). This species differs chi(>fly in the posterior 



