318 ANNALS OF THE CARNEGIE MUSEUM. 
might be called bean-shaped. No hooks are present. Length 0.19; 
height 0.10 mm. (see Plate XIX, fig. 7). 
Color of soft parts whitish. Foot yellowish white, basal part 
(abdominal sac) gray or blackish. Gills gray or grayish white. In 
the gravid female, the marsupium is white or red. Mantle more or 
less suffused with black, whitish toward margins and front parts. Its 
edge has alternating chestnut-brown and black spots. Anal opening 
inside of this maculated edge with a white, followed by a black band. 
Genus FRIERSONIA gen. nov. 
Shell subelliptical, without distinct posterior ridge. Disk not 
sculptured. Beak-sculpture of the double-looped pattern, consisting 
of six to eight fine bars, of which the later ones are distinctly double- 
looped, and the latest are interrupted (unconnected) in the middle. 
Epidermis greenish-yellow, with rather distinct, simple rays. Male and 
female shells hardly different. 
Inner lamina of inner gills connected with abdominal sac. Edge 
of mantle in front of branchial slightly lamellate, with fine and distinct 
crenulations, disappearing gradually in front, but without papille. 
A brown streak of pigment along this part of the edge. Marsupium 
consisting of many ovisacs, occuping the larger posterior section of 
the outer gill. When gravid, the ovisacs swell very little, and they are 
only slightly compressed in the basal part, which is largely enclosed 
between the lamine of the gill. The ovisacs reach considerably 
beyond the edge of the gill, and in this region they are curved backward 
in a peculiar manner, subcylindrical, and tapering toward a point 
directed backward at the hind end of the marsupium. The marsupium 
has also a remarkably sharp edge. Placentz not very solid. Glochidia 
lying all through the placental mass, of medium size, and subovate in 
shape. 
Type F. iridella (Pilsbry and Frierson). 
According to the arrangement in the key (p. 304) this genus would 
appear to fall into the same group with the preceding genera. But 
this is hardly the case. It has in common with the genera with which 
it has been associated in the key only the fact that the marsupium is 
not of the simple kidney-shape shown by the genera which follow in the 
key. The sharp edge of the marsupium, its posterior point, and the 
recurved ovisacs are quite unique. For the present, I do not under- 
stand the meaning ot this structure, but it may be connected with the 
