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. Manlle 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 papillae. 

 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 laminae 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. Placentae 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 of this structure, but it may be connected with the 



