NAIADES OF MISSOURI IOI 
nae, in that the morphology of the Lampsiline glochidium would 
indicate a reversion to the primitive type as is the natural course 
in the cycle of evolution. Thus on the basis of glochidial characters, 
the Family Unionidae may be grouped as: 
1 ANODONTA, bearing non-conglutinated glochidia, spadi- 
form, spined. 
2. PrRoprera, bearing conglutinated glochidia, celtiform, 
spined or spineless. 
3. Unto-LAmpsILis, bearing conglutinated glochidia, apron- 
form, spineless. 
The key to the whole situation governing the approach to 
the mcdern arrangement is in the differentiation of structures for 
the benefit of the embryos; e. g., large palpi for the Umnioninae, 
marsupial water tubes (secondary) and also large palpi for Anodon- 
tinae, but, best of all, an adjustment of marsupium near to a special- 
ized mantle edge in form of flaps, papillae, tentacles, etc., as 
shown in Lampsilinae. 
I—Sus-Famity Unioninae Ortmann. 
1911a— Unioninae Ortmann. An. Car. Mus., IV, pp. 335-336; 1912b 
An. Car. Mus. VIIL, pp. 236-277. 
ANIMAL CHARACTERS:—Branchial opening rather sparingly 
papillose; anal smooth to finely crennulate; supra-anal usually 
present separated from anal by very short or moderately long 
mantle connection; no tendency to form tubular siphonal openings; 
inner laminae of inner gills free from visceral mass; palpi usually 
very large and long, marsupium occupying all four gills or by the 
two outer ones, when gravid not much swollen, ventral edge 
pointed, never bluntly distended and secondary water-tubes 
never developed lateral to the ovisacs within; mantle edge antero- 
ventrad to branchial opening, smooth; glochidia of the Lampsilis 
type, apron-shaped, small to medium, semicircular or semielliptical, 
ventral margin rounded, without spines; conglutinates well 
formed. 
SHELL, CHARACTERS:—Forms of shell various, usually thick; 
disk smooth to very profusely scuptured; beaks usually scuptured 
with concentric or zigzag ridges; hinge teeth very highly developed, 
cardinals and laterals never lacking; scars well impressed. 
MISCELLANEOUS REMARKS:—The soft anatomy of the species 
of this subfamily are rather constant. However, its shell characters 
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