THE NAIADES OF MISSOURI 251 
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lavender; sexual dimorphism not very distinct; the biangular 
character climed for posterior end of male shell not constant. 
Sex Length Height Diameter Um. ra. Locality 
Cer7o RTOS: x. .72mm) 0:26 (Big Mud Lake) 
Cal 7ae TOs mek. 55’ 0.26 (Platte R.) 
OeTOO ks OF) 8X4 20; *" 80220 (eee t})) 
Pease So 155. Sa 255, 0.20 (102 River) 
The juvenile shell is very flat, a very beautiful wine-colored 
epidermis marked with bright brown rays: beaks are coarse, 
marked with the characteristic sculpturing of adult shell except 
the later bars are down on the upper part of the disk; nacre bluish. 
MISCELLANEOUS REMARKS:—This species is both fluviatile 
and lacustrine for this state. Observation of aquarium specimens 
discharging sperm proves this species a gonochorist—a character 
this is opposite to the congeneric species and type of this group, 
compressa Lea. The author has also observed this species to be 
gravid with glochidia from November to April and, in most 
instances, has noted early and late embryos mingled with the 
glochidia in the same individual at the same time. This species 
is very common in North Missouri where it grows very large in 
the lakes, but is uncommon and dwarfed in Central Missouri and 
is not found at all in the clear, swift water-streams of South Mis- 
souri. Complanata is so distinct from other alated forms that there 
should be no confusion. It differs from Proptera alata (Say) in 
that the latter is dimorphic more inflated and has a purple nacre. 
There is such difference between this species and the type (S. 
compressa) that it may well deserve its subgeneric name, Pierosygna 
Raf. (1813), that Simpson applied. 
Symphynota costata (Rafinesque). 
(‘Fluted Shell,’”’ ““Squaw Foot,’ ‘“‘Sand Mussel.’’) 
Pl. XXII, Figs. 71 A—F. 
1820—Alasmidonta costata Rafinesque, Ann. Gen. Sci. Brux., p. 318, 
PR LAA figs 155) 16: 
1823—Alasmidonta rugosa Barnes, Am. Jour. Sci. and Arts, p. 278, 
Dis ackli, fig. 21- 
1900b—Symphynota costata (Raf), Simpson, Proc. Nat. Mus., XXII, 
p. 665. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Anal opening slightly crenulated 
on inner margin; supra-anal moderately separated from anal; 
