112 THE NAIADES OF MISSOURI 



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 to the Mississippi Lowlands of South- 

 east Missouri. Very few Anodontac are reported for vSouth Missouri 

 where lacustrine conditions are rare. 



Anodonta grandis Say. 



("Floater.") 



PI. VII, Fig. 75; PL XXIII, Figs. 7S ^4 and B. 



i&2g— Anodonta grandis Say, N. Harm. Diss., II., p. 341. 

 1852 — Anodonta opaca Lea, Rr. Am. Phil. Soc, X, p. 285, pi. XXV, 

 fig. 46. 



ANIMAL CHARACTERS. 



Nutritive vStructurES: — 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 longe'r, 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, 



