oon ANNALS OF THE CARNEGIE MUSEUM. 
with fine crenulations. It is defined on the inner side by a narrow 
stripe of black pigment. In the male this lamella is also present, but 
much weaker. Farther in front the edge of the mantle is smooth. 
Palpi small, normal, their posterior margins connected only at the 
base. 
Gills short and broad, the inner ones broader. Diaphragm normal. 
Inner lamina of inner gills entirely connected with abdominal sac. 
Anterior attachment of gills as usual. 
Septa and water-tubes in both gills normally developed. Mar- 
supium restricted to a small section in the posterior half of the outer 
gill, leaving more than half of the anterior portion and a small posterior 
section non-marsupial. Ovisacs fifteeen to twenty (in my specimens); 
when charged not narrower than the normal water-tubes in the longi- 
tudinal direction, but expanding in the transverse direction, so that 
their lumen becomes lanceolate and compressed, the whole mar- 
supium thus appearing swollen and kidney-shaped. The marsupium 
extends considerably beyond the original edge of the gill, and about 
three-fourths of the length of the ovisacs is within the lamine of the 
Fic. 20. Obovaria retusa (Lamarck). Gravid female, from Ohio River, Port- 
land, Meigs Co., O. (Carn. Mus., No. 61, 4,773.) 
gill, while one-fourth lies beyond the latter. Edge of marsupium blunt, 
without pigment. Placente not well developed; eggs and glochidia 
rather loose. 
Glochidia rather large, suboval, without hooks. Length 0.22; 
height 0.27 mm. (see Plate XIX, fig. 9). 
Color of soft parts whitish, only edge of mantle brown, with a black 
streak in front of the branchial. Charged marsupium whitish. 
