232 Annals of the Carnegie Museum. 



Outer lamina of outer gills not entirely connected with the mantle, 

 but its posterior part is tree 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 laminae 

 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 

 (19106, p. 181), who created for it the new genus Pseud it nio. Although 



7 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. 



