'i 



lOO THE NAIADES OF MISSOURI 



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 



9 170 X 105 X 72mm 0.26 (Big Mud Lake) 



c?' 175 X 105 X 55 " 0.26 (Platte R.) 



9 100 X 65 X 29 " 0.20 ( " " ) 



9 88 X 55 X 25 " 0.20 (102 River) 



The juvenile shell is very fiat, 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 (5. 

 compressa) that it may well deserve its subgeneric name, Pierosygna 

 Raf. (18 13), 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, 



PI. LXXXII, fig. 15, 16 

 1823 — Alasmidonta rugosa Barnes, Am. Jour. Sci. and Arts, p. 27S, 



pi. XIII, 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; 



