ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 319 
Lea has figured this “flap” of Lampsilis radiata (Observ. II, Pl. 15, figs. 48 
and 49) and of L. ventricosa (Observ. VII, Pl. 30, fig. 107), and he calls special 
attention in L. radiata to its different shape in different individuals. Indeed in 
his two figures (figs. 48 and 49), there is a great difference in so far that in fig. 48 
the anterior prolongation of the flap is not seen. But disregarding the possibility 
that this figure may be inaccurate, the condition shown in fig. 48 may be either 
abnormal, or the anterior end of the flap may be 
injured, or it may not be fully expanded. (1 think 
the latter is very likely the case.) Fig. 49 is rather 
correct, and also the figure of the flap of L. ventricosa. 
I have repeatedly observed this flap in life, and 
have seen it in function. I made the best observa- 
tions in the case of L. ventricosa and multiradiata. 
When the animal is undisturbed, and the posterior 
end of the shell is gaping, we notice, in the gravid 
female, that the marsupia, which are easily recog- 
nized, are pushed outward, so that they project even 
a little beyond the shell (already observed by Lea). 
They show below and in front of the branchial open- 
ing (See fig. 7). The lamellar expansions of the in- 
ner edge of the mantle occupy exactly the place, where 
the marsupia are visible, and are expanded on both 
sides of the latter, projecting beyond the margin of 
Fia. 7. 
Lampsilis ventricosa (Barnes). 
th : Shell of gravid female, seen from above and 
e shell and beyond the marsupia, forming a lateral jenina, showing: a, anal opening; b, bran- 
wall on each side of the latter. In addition, the free chial opening; m, marsupia; mt, mantle; 
flaps are fully expanded, appearing as prolongations *"* / Se ae 
of the lamellar portions, floating free in the water. oat : 
This whole apparatus performs rhythmical, wave-like contractions, beginning at 
the posterior end, and ending at the free tips of the flaps. The contractions follow 
each other in quick succession (two to three in a second), and must produce a very 
lively current of water over the exposed edges of the marsupia. The position of 
the shell being generally much tilted, the animal almost ‘‘standing upon its head,” 
and the shell being directed with its anterior end against the current, the flaps 
float horizontally in and with the current. I once (Sept. 15, 1909) had a chance 
to depict the flaps in action, standing knee-deep in the water of the Allegheny 
M4This is suggested by the generally poor character of the figures on this plate, which are extremely superficial and un- 
satisfactory. 
