ORTMANN: FAMILIES AND GENERA OF NAJADES. 309 
specimens free, except in front, where it is connected for a short dis- 
tance in the female, and for a somewhat longer distance in the male. 
The glochidia are like those of P. phaseolus, but slightly larger. 
Length 0.18; height 0.22 mm. (see Plate XIX, fig. 5). 
The color of the soft parts is the same as in P. phaseolus. Mar- 
supium blackish purple, pale along the beaded edge, with black mark- 
ings like those in P. phaseolus. 
This species is placed by Simpson (19008, p. 591) in the letras 
dus, but he states that the soft parts were unknown to him. If we 
disregard the peculiar sculpture of the posterior slope of this shell, the 
structure of the hard parts is very similar to that of P. phaseolus. In 
some shells of P. swbtentus in the Carnegie Museum I have even seen 
the slight depression inside of the shell, which corresponds to the mar- 
supium.,*® 
Genus OBLIQUARIA Rafinesque. (1820.) 
(Simpson, 1900), p. 610.) 
Shell rounded oval, inflated. Disk with a row of large knobs, 
running from the beak to the center of the base, those of one valve 
alternating with the knobs of the other. Posterior slope corrugately 
sculptured. Beak-sculpture consisting of two or three rather heavy, 
but not sharply defined, concentric bars, which seem to be continued 
by the knobs of the disk. Epidermis greenish-yellow to brown, 
painted with numerous, delicate, wavy, and broken rays, which may 
be entirely absent. Male and female shells essentially alike. 
Inner lamina of inner gills free, except at the anterior end. Edge 
of mantle not differentiated in front of the branchial. Marsupium 
consisting of a few (generally less than ten) ovisacs, occupying a 
position just behind the center of the outer gill, beginning near the 
base of the gill, and reaching far beyond the edge. Thev are large, 
subcylindrical, and slightly curved, and have the rather solid placente 
of the same shape. Glochidia lying all through the placental mass, 
of medium size, almost subcircular. 
Type O. reflexa Rafinesque. 
Obliquaria is a primitive genus of the Lampsiline, which, in order 
to solve the problem of the aération of the glochidia, has reduced the 
36 Sterki (1898, p. 31, and 1903, p. 103) describes in Ptychobranchus ‘‘a deep, 
oblique sulcus on the inside of each valve in the female, the space occupied by the 
marsupium.’’ This sulcus very often consists of a series of impressions correspond- 
ing to the marsupial folds. The same feature is observable in P. subtentus. 
