Ortmann; Families and Genera 01 Najades. 307 



scpi. i of the non-marsupial gills as usual. Marsupium formed by 

 the outer gills in almost their whole length; only small sections are lefl 

 free anteriorly and posteriorly; bu1 in young individuals larger sections 

 arc non-marsupial. In the basal half the whole outer gill is non- 

 marsupial, and has rather wide water-tubes, but the marginal half 

 becomes marsupial, with much narrower water-tubes (ovisacs), and 

 along the edge of the gill the ovisacs bulge out beyond it. This 

 bulging out is only moderate. The placentae are in the distal half of 

 the gill; they are subcylindrical and club-shaped, being thicker toward 

 the edge. The whole marsupium is thrown into a number of folds, 

 increasing its surface, and further, in the distal part of the gill, the 

 filaments are stretched or flattened out, so that the membranes en- 

 closing the placenta? become much thinner in this region than usual. 

 Along the edge of the marsupium, the protruding ovisacs appear as a 

 folded series of beads. The number of the ovisacs and of the folds is 

 variable, and increases with age. Also in the sterile female the 

 beads and folds are indicated on the edge of the marsupium. 



Placenta? quite solid and permanent. They are discharged whole 

 through holes formed at the end of the ovisacs (repeatedly observed). 

 A brown stain is developed in the placenta?, chiefly on their surface, 

 which possibly indicates a hardening of the gelatinous matter. The 

 eggs and glochidia are imbedded uniformly through the placental 

 mass, but they are most crowded at the swollen ends. 



Glochidia (see Lea, Obs., VI, 1858, pi. 5, fig. 12; 34 and Ortmann, 

 19116, pi. 89, fig. 14) rather small, subovate, without hooks, higher 

 than long. Length 0.17; height 0.19 mm. 



Color of soft parts whitish, foot grayish, gills whitish, or grayish 

 brown. Edge oi mantle brown, broadly black posteriorly. Marsu- 

 pium, when charged, blackish or purplish brown, inclining sometimes 

 more to blackish, sometimes more to purple. Beads at edge more 

 vividly colored, red or purple. A line of black markings near the 

 edge, immediately below the protruding beads, on each side. 



34 The poor quality of Lea's figures of the glochidia is clearly shown in this in- 

 stance. The figure of the glochidium of phaseolus (fig. 12) stands next to that of 

 Eurynia recta (fig. 11), and is distinctly larger than the latter, while actually the 

 glochidium of E. recta is by far the larger of the two. Also the outlines of these two 

 glochidia are not quite correctly rendered. 



