2ae ANNALS OF THE CARNEGIE MUSEUM. 
Outer lamina of outer gills not entirely connected with the mantle, 
but its posterior part is free for about one-fourth, or slightly less, of its 
length. Inner lamina of inner gill free from the abdominal sac with 
exception of its anterior end. Behind the foot, the two inner lamine 
of the inner gills are connected. Thus the diaphragm (separation of 
branchial and suprabranchial-cloacal cavities) is formed only by the 
gills, and it is incomplete posteriorly, and does not reach the margin 
of the mantle, although the medially united free ends of the gills 
project to near the margin of the mantle. 
Gills without water-tubes and without septa. The interlaminar 
connections are patch-like, irregular in shape and position, and only 
here and there a diagonal arrangement, from the base toward the 
edge and forward, is indicated, which, however, does not follow the 
direction of the gill-filaments, and does not form continuous septa. 
Color of soft parts grayish, inclining to blackish. Foot brown, 
paler on edge; through the middle runs a black band, sharply marked 
off from the whitish abdomen, but gradually shading into the brown 
of the foot. Gills brownish-gray anteriorly, shading to black pos- 
teriorly. Mantle brownish-white, edge black, broadly so behind. 
From the posterior end of the attached part of the outer lamina of the 
outer gill there runs to the posterior margin of the mantle a white line, 
bordered below with black. 
No gravid females are at hand, and thus the writer cannot say any- 
thing about the marsupium and the glochidia. However, these have 
been described by others (see Harms, 1907 and 1909). The marsupium 
is formed by all four gills,?7 and the glochidia are very small (0.0475 
mm.), semicircular, globular, without true hooks, but with a number 
of small teeth on the ventral margin. 
The breeding season in Pennsylvania is in June and August (Conner, 
1909, p. 112), in Germany in July and August (Harms, 1907, p. 814), 
and probably twice in succession during this time (Harms, 1909, p. 
332). 
Margaritana sinuata (Lamarck). 
The anatomical structure of this species has been described by Haas 
(1910), p. 181), who created for it the new genus Pseudunio. Although 
* Simpson (1900), p. 674) says that the marsupium is formed only by the outer 
gills, and refers (footnote 2) to von Wahl. I have consulted this paper (Wahl, 
1855), but cannot find in it anywhere a description or mention of the marsupium of 
Margaritana. 
