356 ANNALS OF THE CARNEGIE MUSEUM, 
mantle in front of the branchial is also somewhat distant from the 
toothed outer edge, and bears four to ten, rather distant, subconical, 
small papilla, which are smaller than the papillae of the branchial, 
and decrease in size forward. Along this part of the edge runs a 
black streak, and the papillae also are black or brown. The space 
between the two edges is blackish-brown, lighter toward the outer 
edge. Before the middle of the lower margin is reached, the two edges 
approach each other, and thence forward are normal, the inner one 
smooth. In the male, the two edges are subparallel and close together, 
as is normal, and there are only a few small papille in front of the 
branchial. 
Posterior margins of palpi connected at base only. Gills and dia- 
phragm of normal structure. Inner lamina of inner gills entirely 
connected with abdominal sac. 
Marsupium formed by over half of the posterior part of the outer 
gill, with hardly any non-marsupial part behind, greatly swollen, 
kidney-shaped, higher in front 
than behind, and slightly de- 
formed to suit the shape of the 
shell, presenting a broad face 
outwardly and downwardly, and 
having a blunt edge toward the 
median line of the animal, where 
the two marsupia come into 
contact, Margin of marsupium 
Fic. 27. Truncilla triquetra Rafinese without pigment. Ovisacs nu- 
que. Gravid female, from Allegheny 
River, Aladdin, Armstrong Co., Pa. ok : ; 
(Carn. Mus., No. 61, 3,358.) Coll. Sept. Chidium of medium size, almost 
18, 1908. semicircular; length and height 
0.2Imm. (See Ortmann, 19110, 
pl. 89, fig. 24; Lea’s figure, Obs., VI, 1858, pl. 5, fig. 19, is not correct.) 
Color of soft parts whitish. Margin of the mantle with black spots 
merous, thirty to forty. Glo- 
in the posterior parts, black inside of the branchial opening, and with 
black streak in front of the latter, farther in front brown. 
The characteristic structure of the inner edge of the mantle is very 
poorly developed in this species, and if it were not for the other 
species, its significance would hardly be realized. Nevertheless, 
according to shell characters, this is a true Truncilla (being besides 
the type). 
