30t> 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). Placentae very solid. Glochidia suboval, 

 rather small. 



Type: P. phaseolus (Hildreth). 



This genus, in many respects, is the most primitive among the 

 Lampsilince, 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, 191 1). 



Bradytictic, gravid from autumn to spring. 



The soft parts have been described and figured by Lea (Obs., VII, 

 i860, pi. 29, fig. 101) and Lefevre and Curtis (1910, pi. 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 

 papillae, 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. 



