ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 335 
2. Family Untonip# (d’Orbigny), Ortmann (Nautilus, February, 1911). 
Diaphragm complete, formed by the gills; posteriorly the outer lamina of the 
outer gill connected with the mantle to its posterior end; anterior end of the inner 
gills separated from the palpi by a gap; branchial and anal openings sharply 
separated from one another by the diaphragm; anal opening very rarely not closed 
above and without supra-anal, generally closed and with a supra-anal opening 
(which very rarely may be obliterated); gills with water-tubes and distinct, con- 
tinuous interlamellar septa, running parallel to the filaments. Marsupium in all 
four gills, or only in the outer gills; larva a glochidium. Shell of very variable 
shape; sculpture of the beak more or less reduced, of various types, but originally 
of the concentric or zig-zag pattern; hinge-teeth perfect or imperfect; epidermis 
plain or with color-markings. 
1. Subfamily Unrtontna (Swainson) Ortmann. 
Inner lamina of inner gills generally free from the abdominal sac (sometimes, 
in extralimital forms connected); supra-anal opening sometimes not separated from 
the anal, normally present, the closed part rather short; branchial opening well- 
defined; no papille or flaps on edge of mantle in front; marsupium formed by 
all four gills, or by the outer gills only; edge of marsupium always sharp and not 
distending; water-tubes not divided in the gravid female; glochidium semi-elliptic 
or semicircular, without spine; shell generally heavy and solid, rounded to elon- 
gated, mostly with dull-colored epidermis; sculpture of the beak generally rather 
indistinct, concentric, or pustulous, or with indications of double loops or zig-zag 
bars; hinge always complete, with rather strong teeth; generally no difference of 
sex shown in the shell. 
GENERA 
a, All four gills serving as marsupium; anal and supra-anal opening separated, but separation often deciduous; 
shell of various shapes, always rather heavy, outside smooth or with sculpturings. 
Genus Quadrula Rafinesque. 
a. Only the outer gills serving as marsupium. 
b', Supra-anal not separated from the anal opening; sculpture of the beak consisting of numerous, fine, 
irregular corrugations; shell rounded; beak-cavities very deep; nacre dark violet or purple. 
Genus Rotundaria Rafinesque. 
}?, Supra-anal opening separated from the anal; sculpture of the beak consisting of few, generally concen- 
trie ridges; shell rounded or elongated; beak-cavities of medium depth, or shallow. 
cl. Shell oblique, ovate, or rhomboidal, with prominent beaks, which are placed rather anteriorly; 
color of epidermis brown to light, generally not very dark, often with rays; nacre varying from 
light red to white. Genus Pleurobema Rafinesque. 
