PLEUROBEMA 809 
of the epidermis is soft and silky while in @sopus it is hard 
and shining. 
I change Lea’s name because Lamarck previously applied 
the name Unio waricosa to what is no doubt, Alasmidonta mar- 
ginata. Mr. T. G. Lea, of Cincinnati, took many specimens of 
this species, the shells of which he sent to Dr. Lea, and in 
several of them he has written in pencil “not charged” or 
“ovaries charged,” with the date, but neither of them seems 
to have described the animai. I am somewhat at a loss to 
know where to place this curious form. The young are much 
like those of Ouadrula solida, and do not show the swellings 
until the third or tourth year, and occasionally the adult shell 
is nearly smooth. 
PIEUROBEMA COMPERTUM (Frierson). 
“Shell medium in size. Apparently dimorphic, the females 
(?) being broader behind than the males and more rounded, 
the males (?) being somewhat triangular and pointed behind, 
beaks high and well forward (their sculpture not seen). Epi- 
dermis dirty vellow, darker before (as in circulus). Basal 
outline rounded and, in the females, expanded in the middle; 
shell not very much inflated. The posterior ridge is rounded 
and becomes more and more inflated with age. ‘The posterior 
area is narrow, with several more or less well-defined lines 
from beak to margin. Down the centre of the disk runs a row 
of pustules, larger in the females, as well as more numerous. 
Inside, the nacre is white, quite thick in front, as far back as 
the centre, or row of pustules, from thence it becomes remark- 
ably thin in comparison, producing a trough-like excavation 
from beak to posterior base. Teeth erect and fairly stout ; 
two cardinals and two laterals in the left valve and one each in 
the right. 
Length 2.3, height 2.1, diam. 1.3 inches.” (Frierson) 
Habitat: Clinch and Holston rivers. 
Type locality not specified. 
Unio compertus Frierson, Naut., XXV, ro1t, p. 53, pl. 1, 
middle and lower figures. 
