W. Stimpson on the so-called Melanians of N. America. 45 
recently confirmed by Lucaze-Duthiers." Indeed, wherever the 
generative organs of any of the Prosobranchiates have been sub- 
mitted to a thorough examination, the sexes have been found to 
be distinct, and it may now be considered safe to conclude that 
they are so in all of them. 
In the groups to which the Melanians have been supposed to 
) n 
might well have been expected. Yet I did not succeed in find- 
ing it in any of my specimens; and the best endeavors to dis- 
criminate the sexes by dissection of the internal organs of gene- 
ration were baffled by their similarity in all individuals, until the 
microscopic test was applied, when all doubts were removed b 
the discovery of ova in that organ in some individuals, and of 
Spermatic particles in others, while the two were never 1. 
found together; proving the organ in one case to be an 
Ovary, and in the other a testis. The form of the sper- 
matic particles in Velania virginica is nearly represent- 
in fig. 1; the tails should be more slender. 
The fact being thus ascertained that the sexes are 
distinct in these animals, notwithstanding the agreement 
in form of the respective organs of generation, and the 
absence of a copulatory organ in the male, search was made for 
some external character by which the sexes might be distin- 
guished, and it was shortly found that all those individuals in 
Which the genital organ contained ova, had a conspicuous slit or 
sinus in the right side of the foot, about midway between the 
tentacle and the operculigerous lobe; while in those : 
in which the organ contained spermatozoa, this sinus : 
Was entirely absent. Fig. 2 illustrates the position 
of the sinus in the female of Mudalia dissimilis. 
_ The female Melanian, then, may be distinguished 
m the male by the presence of this sinus. It_ 
Consists of a deep pit on the impressed line mentioned in the 
description of the body and foot, from which a canal, formed 
by a fold of the superior parieties of the pedal muscles, extends 
downward nearly to the margin of the pedal dise. My observa- 
tions have not extended far enough to enable me to ascertain 
u ; Siti 209. 
- rete on vis [eh sangied te sa rere Melaniidew by Lea. (Observa- 
tions on the genus Unio, etc, vol. ix, (1862), p. 40). 
