ORTMANN: monograph of the naiades of PENNSYLVANIA. 133 



Lasmigona (Pterosyna) complanata (Barnes) (1823). 



Sympkynota complanata (Barnes) Simpson, 1914, p. 490. 



Plate IX, fis. 7. 

 Records from Pennsylvania: 



Ortinann, 19096, p. 196. 



Characters of the shell: Shell large; rather thin when young, moderately solid 

 when old. Outline broadly ovate, subrhomboidal, not elongate, only a little longer 

 than high. Anterior end rounded, posterior obliquely truncate. Lower margin 

 convex, less so posteriorlJ^ Upper margin nearly straight, strongly ascending 

 posteriorly^, forming a distinct angle with the posterior margin, and projecting so 

 as to form a vej-y distinct wing, the upper margin of which is symphynote. The 

 wing is best developed in j'oung specimens. Beaks not prominent, placed in front 

 of the middle of the shell. Beak-sculpture consisting of four to five rather distinct 

 and sharp bars, the first one or two simply curved, the others strongly double- 

 looped, with the anterior loop round and wide, the posterior narrower and angled, 

 and with a sharp, re-entering angle between them. Shell flat and greatly com- 

 pressed, with an indistinct, blunt and broad posterior ridge. The posterior slope 

 is alate and strongly compressed, and in many cases is ornamented with irregular 

 ridges running toward the posterior margin, which, however, may be entirely 

 absent. Disk in front of posterior ridge smooth, without sculptm-e. 



Epidermis yellowish to greenish brown; when young with indistinct traces of 

 green raj's, which become entirely obsolete in older shells, of which the epidermis 

 is lighter or darker brown, often blackish. Sometimes there is some dark green in 

 the epidermis. Growth-rests more or less distinct, often marked by darker color. 



Hinge-teeth partly obliterated. Pseudocardinals present and rather heavy, 

 and quite variable in shape. Interdental projection variable, sometimes rather 

 distinct; in other cases weak, and often entirely absent. Lateral teeth practically 

 absent, indicated only by vestigial blunt ridges. The conformation of the hinge 

 in this species is extremely and remarkably variable. Beak-cavity shallow. 

 Dorsal muscle-scars in the beak-cavity. Nacre white, sometimes lightly tinted 

 with cream-color toward the beak-cavity. 



No differences in the shape of the shell in the two sexes. Baker (1898o, 

 p. 60) and Scammon (1906, p. 332) say that the male is more compressed than the 

 female. This is not at all correct, as is easily seen by comparing nos. 2, 3, and 4, 

 and nos. 5 and 6 in our table of measurements. 



