THE NAIADES OF MISSOURI 263 
really only represented in this-state by A. grandis and Danielsii. 
However, the latter, even may only be a creek form of grandis. 
A few other species, reported for this state under this genus, have 
doubtless received their names without deserving them and hence 
will only receive passing notice. The members of this group being 
lacustrine, they are limited more to the lake distinct in Northwest 
Missouri, to that portion of Central Missouri where lakes, ponds 
and sloughs abound, and e the Mississippi Lowlands of South- 
east Missouri. Very few Anodontae are reported for South Missouri 
where lacustrine conditions are rare. 
Anodonta grandis Say. 
(‘‘Floater.’’) 
FeV hag 552) Pi XATIN, Fags. °75° A and B. 
1829—Anodonta grandis Say, N. Harm. Diss., II., p. 341. 
1852—Anodonta opaca Lea, Rr. Am. Phil. Soc., X, p. 285, pl. XXV, 
fig. 46. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening with rather 
long yellowish papillae; anal directed upward, smooth; supra- 
anal separated from anal by long mantle connection, small, almost 
closed in some instances; inner gills wider and longer, inner laminae 
entirely free from visceral moss; palpi very large united antero- 
dorsad about one-half of their length; anterior portion of peri- 
cardial region thick and watery; color of gills usually dark brown, 
mantle edge at siphonal openings blackish, palpi cream to purplish, 
remaining parts mostly tan or soiled white. 
REPRODUCTIVE STRUCTURES:—Marsupium occupying outer 
gills only, when gravid pad-like, distended at ventral edge, secon- 
ary water canals present, undivided ovisacs in center, laminae 
very delicate rupturing at slight touch; sterile marsupia thick- 
ened at edges to allow for distention; glochidium largest on record, 
(0.400 x 0.395mm.), spadiform, spined, russet color, straight 
hinge line; no conglutinates, glochidia held in loose mosses by 
brownish mucus and tangles of crinkled larval threads. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell subovate, large, greatly in- 
flated especially in umbonal region, subalated, subsolid anteriorly, 
