2 2 NAIADES OF MISSOURI 



for intermediate forms not only for Fusconaia, but for other Genera 

 of this vSub-family, Unioninae, especially. All Fusconaia of this 

 State are strictly fluviatile. For the most part the Species of this 

 Genus are hermaphroditic, for all localities. 



Fusconaia undata (Barnes). 



('"Pigtoe.") 

 PL XV. F-igs. 2g A and B. 



1823 — Unio undatus Barnes, Am. Jour. Sci., VI, p. 121, pi., iV, fig. 4. 



.1831 — Unio trigonus Lea, Tr. Am. Phil. Soc, IV, p. no, pi XVI, fig. 40. 



1900b — Quadrula trigona, Simpson, Proc. U. S. Nat. Mus., XXII, p. ,787. 



1900 — Quadrula undata Walker, Nautilus, XXIV, pp. 5-1 1 and 16-24, 



Plates I and I. 

 1912b — Fusconia undata (Barnes) Ortmann An. Car. Mus., VIII, p. 241. 



ANIMAL CHARACTERS. 



Nutritive vStructures — Branchial opening with short 

 brownish papillae; anal slightly papillose, separated from supra- 

 anal by very short, — even deciduous — mantle connection; inner 

 gills larger, inner laminae free from visceral mass; outer gill 

 undulate antero-ventrad, palpi moderately large, connected over 

 half of their length antero-dorsad; most of soft parts yellowish 

 or cream colored. 



Reproductive Structures: — Marsupia formed by all four 

 gills, when charged not distended, lumen of ovisacs subcylindrical; 

 conglutinates same form, light red — even to white — according 

 to age of embryos; glochidium semicircular, medium size, hinge 

 line nearly straight, length and height. (0.160 x 0.155mm), about 

 same. 



shell characters. 



External Structures:^ — Shell trigonal, thick, heavy anteri- 

 orly, disk smooth; beaks high, full, pitched slightly beyond 

 anterior end, sculptured with concentric ridges breaking into 

 nodules at base of prominent umbonal ridge; dorsal line bowed, 

 post-ventral line with long gentle incurve; broad shallow valley 

 in front of post-umbonal ridge; ventral margin bowed in semi- 

 circular form; epidermis greenish to rusty brown or black or 

 mingling of both green and black; rest lines furrowed giving an 

 undulated effect; post-umbonal ridge prominent. 



Internal Structures: — Cardinals single and pyramidal in 

 right, double and roughly socketed in left; laterals double in 



