NAIADES OF MISSOURI 21 



Genus Fusconaia Simpson. 



1900b — Fusconaia Simpson, Pr. U. S. Nat. Mus. XXII, p. 784 (as sect.) 

 1912b — Fusconaia (Simpson) Ortmann, An. Car., Mus., VIII, pp. 

 240-241. 



(Tpye Unio undatus Barnes). 



Animal Characters: — Branchial opening with dense yellow- 

 ish tentacles; anal smooth; supra-anal separated from anal by 

 very short connection, laminae of inner gills free from visceral 

 mass; palpi rather large; all four gills marsupial, ovisacs when 

 gravid subcylindrical ; conglutinates same shape, usually reddish, 

 subsolid and discharged whole; glochidium subovate, somewhat 

 small, spineless; colors of soft parts usually brilliant, such as 

 orange or red. 



Shell Characters: — vShell roundly quadrate or triangular; 

 disk smooth; beaks elevated, sculptured with concentric ridges 

 angled at base of prominent post-umbonal ridge; epidermis 

 reddish to brown with fine, rather interrupted, .rays when young; 

 hinge teeth well developed; beak cavities deep; nacre white. 



Miscellaneous Remarks: — Dr. Ortmann considers this 

 genus the most primitive of the Unionidac and limits it to those 

 species of Simpson's trigona group that possess subcylindrical 

 conglutinates and ovisacs, concentric beak sculpture and smooth 

 disk as the diagnostic features. While the conglutinates of the 

 Fusconaia species may be reddish, yet they may vary from pale 

 pink to white due to their development usually. It is to be noted, 

 however, that when the conglutinates are white all of the anatomy 

 is also white; when the conglutinates are reddish the soft parts 

 will be more yellowish. In this state the following groups may 

 differ morphologically and ecologically as follows: 



1. F. undata: swollen, high beaks, mostly greenish — black 

 epidermis Big Rivers 



2. F. trigona: swollen, lower beaks, mostly reddish epider- 

 mis Medium Rivers 



3. F. flava: flat, low beaks, always reddish epidermis 



Small Rivers 



The second group is not found in very typical form in this 



State, but is represented by intergrading forms. In fact none of 



these Species, representing the above names, are very often found 



typical in Missouri, since this vState seems to be the home mostly 



