THE NAIADES OF MISSOURI 201 
Elliptio dilatata (Rafinesque). 
(‘Lady Finger,’ ‘‘Spike,’’ ‘‘ Pistol Grip.’’) 
Pl. XXI, Figs. 66 A and B. 
1820— Unio (Elliptio) dilatata Rafinesque Monog. of Bivalves of Ohio, 
Ann. Gen. Sci. Phys. Brux. 
1823— Unio gibbosus Barnes, Am. Jl. Sci., VI, p. 262, pl. XI, fig. 12. 
1838— Unio arctior Lea, Tr. Am. Phil. Soc., VI, p. 10, pl. IV, fig. ro. 
1912b—Elliptio gibbosus (Barnes) Ortmann, An. Car. Mus., VIII, 
jo), edges 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES :—Branchial opening small with many 
short, blackish papillae; anal with a single row of low papillae; 
supra-anal separated from anal by short mantle connection; 
gills long and narrow, inner laminae of inner gills free—in some 
instances connected about one-fourth of the way anteriorly; 
palpi short, wide, connected antero-dorsad about two-thirds of 
their length; color of soft parts soiled grayish with area in front 
of branchial opening yellowish, pericardianl region invariably 
reddish brown. 
REPRODUCTIVE STRUCTURES:—Only outer gills are marsupial, 
marsupia moderately swollen in center when gravid, dark tan; 
conglutinates narrowly lanceolate, always whitish; glochidia 
medium size, spineless, hinge line slightly depressed, measure 
0.200 X 0.220mm. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell elongate-ellipsoid, gibbose, 
thick heavy, post-umbonal ridge rounded, inflated; disk smooth; 
beaks flattened, coarsely sculptured with five or six wavy ridges 
more pronounced behind; epidermis dark brown to horn or 
yellowish. 
INTERNAL STRUCTURES:—Cardinals rather low, double in 
both valves; laterals double in left and inclines to double in right 
valve; interdentum very long, cut away in right to receive left 
post-cardinal; umbonal cavities rather shallow; however, deeper 
in female shell; nacre mostly dark purple, varies from all shades 
of purple to salmon and white. 
Sex Length Height Diameter Um. ra. Locality 
Oe ashe kee O50 8 4520 0.260 (Miss. R., Hannibal) 
SiTsOy ke 50% 1298-0 0.255 (Osage R., Osceola) 
OS AZ yr xer Ors x 9.5 0.255 art # 4 ) 
SUMASO. eRe! TG. 0.5 0.250 (Niangua R., Hahatonka) 
