248 THE AMERICAN MIDLAND NATURALIST 
specimens of this form to find it with the same breeding season 
as its parent species. 
Il—Sus-Fami.y Anodontinae Ortmann. 
1911a—Anodontinae Ortmann, An. Car. Mus., IV, p. 336; 1912b, 
An. Car. Mus., VIII, pp. 278-300. 
ANIMAL CHARACTERS:—Mantle edge, antero-ventrad to 
branchial opening smooth without specialized structures; supra- 
anal antero-dorsad to anal opening usually widely separated; no 
tendency toward tubular siphonal openings; inner laminae of 
‘inner gill generally free from visceral mass; region just anterior 
to pericardium of watery composition; palpi very large; mar- 
supia—occupyiug two entire outer gills, when gravid pad-like, 
enormous, tissue thickened at edge to permit transverse distention, 
two water tubes present on either side of an enclosed central 
undivided ovisac and facing outer and inner laminae, these 
laminae very thin and delicate rupturing at the slightest scratch; 
glochidia usually large, spadiform, generally longer than high, 
with a spine at each ventral tip; no well-defined conglutinates, 
but held together in unstable masses by brownish mucus and a 
tangle of larval threads. 
SHELL CHARACTERS :—Shell thin for the most part; disk usually 
without sculpturing; beaks usually coarsely sculptured with con- 
centric or double-looped ridges; hinge variable, teeth completely 
lacking, or, if present, rudimentary or peculiar; beak cavities not 
deep asarule; sexual dimorphism rarely seen. 
MISCELLANEOUS REMARKS:—The members of this group have 
a long period breeding season (bradytictic) due perhaps to their 
origin at a time, as Dr. A. E. Ortmann considers, when a possible 
shortening of the warm season induced them to retain their embryos 
in the marsupia and discharge the glochidia in the spring; hence, 
the constant and admirable adaptation of water-tubes for the 
aeriation of the embryos in the marsupia while being retained for 
that time. This adaptation elevates this group from the primitive 
one and places it more among the modern Unionidae. Even on the 
basis of shell structure, in that the sculpturing, seen on the disk 
of the shells of the Unioninae, is carried back up to the umbona 
region where it is almost exclusively confined, there is sufficient 
evidence for the more modern grouping. ‘The inability of the 
Anodontinae to spread their vavles very wide may account for 
