346 THE AMERICAN MIDLAND NATURALIST 
(Type, Unio cognatus Lea.) 
ANIMAL CHARACTERS:—Anal opening crenulated;  supra- 
anal widely separated from anal; inner laminae of inner gills con- 
nected to visceral mass except for a small posterior slit; palpi 
small; marsupia consisting of several ovisacs at posterior half 
of outer gill that acutely tapers; conglutinates white, undivided; 
glochidia smallest of all Nazades. 
SHELL CHARACTERS:—Shell among the smallest, roundly 
triangular, inflated, flattened on post-dorsal slopes; post-umbonal 
ridge sharply angular; disk smooth; beak rather full, sculptured 
with a few ridges, the latter ones being rather definitely double 
looped; epidermis greenish to yellowish with characteristic paint- 
ings of green arrow-marked rays; female shell slightly more 
inflated post-ventrad; hinge teeth delicate; nacre usually white. 
MISCELLANEOUS REMARKS:—Although this genus stands 
very close to Obovaria and Nephronazas, having essentially identical 
structures of soft parts, yet it deserves this compartment on account 
of its unique form, size and color markings of shell and especially 
upon its glochidial characters, being the smallest on record. The 
only two members of this genus are represented in this State by 
A. donaciformis (Lea) in North Missouri and by truncata (Raf.) 
in Central Missouri. The latter is never found north of the Missouri 
River and the former is rarely ever found in Central Missouri; 
neither have been found by the writer in South Missouri. The 
Osage River bears many intergrades for these two species. 
Amygdalonaias donaciformis (Lea). 
(‘‘Fawn’s Foot,” ‘‘Deer-Toe,”’ “ Zigzag.’’) 
Pl. XXV, Figs. 89 A—D. 
1828—Unio donaciformis Lea, Tr. Am. Phil. Soc., 111, p. 267, pl. 
WAYS GL Slvie5 She 
1820— Unio zigzag Lea, Tr. Am. Phil. Soc., III, p. 440, p. XII, fig. 19. 
1898—Plagiola donaciformis Baker, Moll. Chicago, Pt. I, p. 92, pl. 
XIII, fig, 4; 1900b, Simpson, Proc. U. S. Nat. Mus., XXII, p. 605. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening small with 
numerous papillae; anal indistinctly crenulated; supra-anal 
separated by a long and thick mantle connection to anal; inner 
laminae connected to visceral mass except for a narrow slit 
