THE NAIADES OF MISSOURI I57 



d.'veloped; beaks low, sculptured by the early bars of fine con- 

 centric arrangement and later one of double-looped type — some- 

 times rather nodulous at base of post ridge; sexually dimorphic, 

 the female shell being wider posteriorly by the expansion of the 

 post-ventrad edge of shell. 



Miscellaneous Remarks: — ^With the exception of unique 

 glochidium and more developed hinge this genus stands with 

 Lasmonos. Proptera is represented in this state by the four species : 

 alata, which is found mostly in Central Mo., purptirata which 

 only occurs in South Mo., laevissinia which is mostly restricted 

 to North Mo., and capax which is entirely confined to the Miss- 

 issippi River. The last named species has not been definitely 

 settled within any genus before on account of a lack of an exact 

 determination concerning the morphology of its animal. The 

 extreme inflation of the capax shell, as compared to the compressed- 

 type of the other members of this genus, would seem to shut it 

 out, but glochidial and marsupial characters (besides its similar 

 beak sculpture) are by far more reliable affinities. All the members 

 of this most sharply defined genus are long period breeders. 



Proptera alata (Say). 



("Razor Back," "Rudder Back," "Hatchet Back," 



"Pan Cake.") 



PL IV, Fig. iia. 



1816 — Unto alatus Say, Nich, Encyc, II, pi. IV, fig. 2. 



1898 — Lampsilis alatus Baker, MoU. Chicago, Pt. I, p. 97, pi. XVIII. 



1912b — Proptera alata (Say) Ortmann, An. Car. Mus., VIII, p. 2i33- 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial and anal openings inclined 

 to tubular structure, branchial upcurved, small with numerous 

 papillae; anal smooth thick edges; supra-anal large thick and 

 close mantle connection to anal; inner laminae of inner gills 

 entirely connected to visceral mass; palpi about as wide as long, 

 connected about one-half of their length antero-dorsad; color 

 of soft part tan-flesh color with dark mantle edges and orange 

 colored cerebral ganglion. 



Reproductive Structures : — -Marsupia large, occupying pos- 

 terior half of outer gills, consisting of large ovisacs sulcated ventrad 

 mantle edge antero-ventrad to branchial opening lamelar with 



