306 ANNALS OF THE CARNEGIE MUSEUM. 
looped. Epidermis brownish, usually painted with hair-like rays, 
forming here and there squarish spots. Hinge-teeth well developed. 
Male and female shell alike externally, but internally the female shell 
has an oblique depression for the marsupium. 
Soft parts with the inner lamina of the inner gills variable, free, 
except at the anterior end, to entirely connected, with all intergrades 
between these two extremes. Edge of the mantle not differentiated 
in front of branchial. Marsupium formed by the whole of the outer 
gills, with more crowded septa than the non-marsupial gills. Ovisacs 
only slightly extended beyond the edge of the gill, occupying only the 
marginal part of the gill, rather short, subcylindrical, and club-shaped 
(swollen at distal end); the whole marsupium is thrown into a number 
of folds (six to twenty). Placente very solid. Glochidia suboval, 
rather small. 
Type: P. phaseolus (Hildreth). 
This genus, in many respects, is the most primitive among the 
Lampsiline, but the folds of the marsupium represent a special 
structure. 
Ptychobranchus phaseolus (Hildreth). 
I have seen many specimens from the Ohio and Lake Erie drainages 
in Pennsylvania, and one gravid female from the Ouachita River, 
Arkadelphia, Clark Co., Arkansas (H. E. Wheeler, coll. Febr. 6, 1911). 
Bradytictic, gravid from autumn to spring. 
The soft parts have been described and figured by Lea (Obs., VII, 
1860, pl. 29, fig. 101) and Lefevre and Curtis (1910, pl. 1, fig. 1). 
Edge of mantle closed between the anal and supra-anal, the con- 
nection is short, but was never found missing. The branchial has 
papille, the anal is finely crenulated. In front of the branchial opening 
the inner edge of the mantle is first finely crenulated, but then becomes 
entirely smooth. Palpi of usual shape, their posterior margins con- 
nected for about one-fourth of their length. 
Gills long and moderately wide, the inner the wider. Their anterior 
attachment as usual, with the end of the inner gill slightly in advance 
of that of the outer, but widely separated from the palpi. Diaphragm 
normal, inner lamina of inner gill very variable: generally it is more or 
less free, and may be attached to the abdominal sac only at the anterior 
end, or for a greater distance; but in one case (out of thirty-two) it 
was found to be entirely connected. Thus, in this species, this char- 
acter is inconstant. 
