THE NAIADES OF MISSOURI I59 



SHELL CHARACTERS. 



External Structures: — Shell large broadly elliptical, solid 

 alated post-dorsad; somewhat inflated at middle of disk, beaks 

 low sculptured concentrically and also double-looped; disk not 

 sculptured; epidermis usually black-reddish with broad rays in 

 young specimens; female shells blunt, or even truncate, vertically 

 for its posterior end. 



Internal Structures: — Cardinals erect-double in both 

 valves; laterals also double placed at an upward angle; beak 

 cavities moderately deep; nacre usually purple. 



Sex Length Height Diameter Locality 



9 156 X 117 X 56.5 (Platte, R., Dixon Falls) 



cf 150 X 114 X 53.0 ( " ' Platte City) 



9 115 X 55 X 33.0 (Osage R., Warsaw) 



9 82 X 54 X 26.0 (Grand R., Utica) 



Miscellaneous Remarks: — This species is most typical in 

 North Missouri; the shell is thinner, smaller and rather dwarfed 

 in Central Missouri and is wholly lacking in South Missouri 

 drainage. The writer has only found alata lacustrine on one 

 occasion, but that may have been due to accidental translocation. 

 Breeding records show it to be bradytictic. The writer has observed 

 that most marsupia of this species, when gravid with ripe glochidia, 

 have purplish blotched marsupia; this character, however, is 

 rather inconstant. Alata has a general distribution throughout 

 the Mississippi and St. Lawrence River basins. 



Proptera purpurata (Lamarck). 



("Purple Shell," "Purply," "Buttermilk Shell," Red Shell.") 



PL XXVI, Figs. 92 A—D. 



1819 — Unto purpurata Lamack, An. Sans, Vert., VI, p. 71. 



1900b — Lampsilis purpuratus Smpson, Pr. U. S. Nat. Mus., XXII, 

 p. 568. 4 



1912b — Proptera purpurata (Lam.) Ortmann, An. Car. Mus., VIII, 

 p. 234. 



ANIMAL characters. 



Nutritive Characters: — Identical with those of alata. 



Reproductive Structures: — Marsupium consists of twenty 

 ovisacs placed in posterior half of outer gills; glochidia (according 

 to Lea) ax-head shape — no measurement given. 

 SHELL characters. 



External Structures; — vShell large, rather elongate — ellip- 



