314 . ANNALS OF THE CARNEGIE MUSEUM. 
this part is very small when compared with the prolonged portion. 
The latter curves backward in a circle, and is rolled up spirally, the 
spiral forming about one and a half to two turns, but only the posterior 
ovisacs complete the whole revolution, while the anterior ones stop 
earlier, the first after completing the circle about once. The distal 
parts of the spiral wind up in the direction toward the median line of 
the body, so that in a view from the outside, they are hidden under 
the outer gill and the first whorl of the marsupium. 
The ova fill the ovisacs in the shape of closely packed masses, forming 
distinct and very solid placentae, red in color, rarely white. Glochidia 
rather small, almost semicircular, distinctly longer than high, without 
hooks. Length 0.18; height 0.15 mm. (see Plate XIX, fig. 6). Sterki 
(1898, p. 19) gives the dimensions as length 0.21; height 0.17; diameter 
0.14 mm. He also says that the glochidial shell is ‘considerably 
longer than high and has numerous distinct, crowded, concentric lines 
of growth.”’ I have not seen the latter. The shape of the glochidia 
approaches to a degree, that of Dromus, but the disproportion between 
length and height is much less. 
Color of soft parts whitish. Abdominal sac and mantle suffused 
with black. Edge of mantle brown with black spots, this mottling 
extending all around. Marsupium, when charged, red, or (according 
to Sterki) sometimes white. 
Genus Dromus Simpson. (1900.) 
(Simpson, 1900), p. 614.) 
Shell very much like that of Cyprogenia. Beak-sculpture obsolete, 
described by Simpson as consisting of interrupted, concentric ridges, 
but I have never seen them distinctly. 
Inner lamina of inner gills partly free from abdominal sac, connected 
near the anterior end for about one-third, or more, of the length of 
the abdominal sac. Edge of the mantle in front of branchial without 
special structures. Marsupium consisting of numerous ovisacs, which 
occupy the larger posterior portion of the outer gill, leaving a smaller 
anterior section non-marsupial. The ovisacs are comparatively short, 
subcylindrical, or only slightly compressed, and lie practically entirely 
beyond the original edge of the gill. In older individuals, the mar- 
supium becomes warped and folded. Placentz solid, subcylindrical, 
or slightly compressed, rather short. Glochidia placed chiefly toward 
