ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 317 
Lampsilis parva. In this species, Lea already had described and figured (Ob- 
serv. VII, Pl. 29, fig. 102), what he called a “‘caruncle” on the edge of the mantle, 
just in front of the branchial opening. This is according to him a black, spongy 
mass, which, being quite expansible and retractile, may assume various shapes. 
In the three gravid specimens before me, I see a group of black, projecting papille 
standing upon the marginal thickening of the mantle, which extends about as far 
as the middle of the ventral margin of the mantle. This group of papille is rather 
short, and resembles indeed a ‘‘caruncle,”’ yet does not differ in any essential 
respect from the structures, which will be described in the other species belonging 
here. It is composed of from four to six larger, and some smaller papille, and in 
front of it the inner edge is smooth. 
Micromya fabalis. Lea (Observ. X) calls the edge of the mantle below the 
branchical opening “fringed,” and Simpson (1900, p. 525) says in the generic 
diagnosis of Micromya, that it is ‘fringed,’ and in the female is “‘developed into a 
flap with a distinct, toothed ridge inside.’ In the only (sterile) female of Micromya 
fabalis I have seen, the structure of the edge of the mantle is similar to that of 
Lampsilis parva, only the group of papille extends farther forward, but not quite 
as far as the thickening of the margin of the mantle. The number of papille 
is greater. There are from eight to ten larger ones, and a few smaller ones, and 
they are further apart from each other than in L. parva. In the male the same 
structure is present, but the thickening is very slightly developed, and the papille 
are decidedly smaller, and occupy a shorter space on the edge. 
Lampsilis iris. The mantle of this species (as novi-eboraci) has also been 
described by Lea (Observ. X) as “‘fringed,”’ and he says that there are large, distant 
papilla. This is quite correct. I observe in my specimens, that in the female 
there are from four to ten (according to age) very large, conical papillz upon the 
inner edge of the mantle in front of the branchial opening. There are a few smaller 
papille between the larger ones, and the latter are rather remote from each other, 
and are placed at irregular intervals. This row of papillee extends forwards for a 
considerable distance, but not quite as far as the middle of the ventral margin. 
It stops very suddenly, and beyond this point the inner edge of the mantle is only 
finely crenulated or smooth. In the male, the papillee are much smaller. 
Lampsilis nasuta. The female agrees with that of Z. iris in the presence of 
papille, but the latter are very small, fine, and crowded, forming a rather regular 
row, running forward almost to the middle of the ventral margin, where they dis- 
appear rather gradually, and pass into the smooth anterior part of the inner edge 
of the mantle. In this species the inner edge in front of the branchial opening is 
