146 THE NAIADES OF MISSOURI 



(Type, Unto 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 Naiades. 



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 Ohovaria and Nephronaias, 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. donacijormis (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 — Unto donaciformis Lea, Tr. Am. PhiL Soc, iii, p. 267, pi. 

 IV. Fig. 3. 



1820 — Unio zigzag Lea, Tr. Am. PhiL Soc, III, p. 440, p. XII, fig. 19. 



1898 — Plagiola donaciformis Baker, MoU. 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 



