THE NAIDAES OF MISSOURI 199 
ventrad, inner wider but not much longer, inner laminae almost 
entirely free from visceral mass; palpi medium size; color of soft 
parts whitish suffused with black; only outer gills marsupial; 
glochidia small, suboval, spineless. 
SHELL CHARACTERS:—Shell thick, heavy, subsolid, rhomboid- 
ovate, longitudinal axis straight, disk smooth, beaks rather low, 
not near anterior end, sculptured with a few fine concentric ridges 
angled at‘the base of the post-umbonal ridge; epidermis brown to 
black, faintly rayed or rayless; hinge teeth heavy; nacre varying 
from white to deep purple and violet. 
MISCELLANEOUS REMARKS:—This genus falls into two groups 
for this State. The first group is represented by E. nigra (Raf.) 
which possesses a heavy subquadrate of subtrapzoidal type of 
shell but with obscure beak sculpture; the second group is repre- 
sented by E. dilatata (Raf.) which has more of an elongate, gibbosed 
shell with a beak sculpture of thick, heavy, ridges running parallel 
to the growth lines. The two other groups of this genus (that is, 
beadletanus and complanatus groups) are not found in Missouri, 
the former being mostly a representative of some gulf states and 
the latter of the immediate Atlantic drainage. Dr. Ortmann 
used “‘Filiptio’’ as a generic name available for the ‘‘ American 
Unio” and employs the original name, ‘‘ Unio,’ in the sense of 
the “European Unio’’. The soft parts of this genus being practi- 
cally indentical with those of the genera immediately preceding, 
the species are indicated entirely on the basis of peculiar shell 
characters. 
Elliptio nigra Rafinesque.’ 
(“Elephant’s Ear,’’ ‘‘ Pink.’’) 
Pl. XXI, Figs. 64 and 65 A and B. 
1820—Unio (Elliptio) nigra Rafinesque, Ann. Gen. Sci. Brux., V, 
D200, :pl.) LXeCX, figss)a1—z. 
1823— Unio cuneatus Barnes, Am. Jl. Sci., VI, p. 263. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening large, well set 
t Simpson (1900 b, p. 706) applied the name ‘‘ Unto crassidens Lamarck”’ 
to E. nigra Raf., but as previously stated under the description of Mega- 
lonatas (1V, p. 124) that close student of Lamarckian types, Mr. Bryant 
Walker, has settled the question by pronouncing U. crasstdens (1819) as 
the so-called U. trapezoides of Lea (1831). 
