THE NAIADES OF MISSOURI . 313 
inflated elliptical shape with the beak sculpture or coarse concen- 
tric bars bent up behind, but, most of all, by its very peculiar 
marsupial characters which are an adaption to its eccentric habit 
of independent metamorphosis. This and Lastena ohiensis are 
the only species on record so far that do not normally possess a 
fish host for the metamorphosis of its larva. This species is not 
so particular about its habitat and hence it has one of the widest 
distributions of any species in the United States. It is strange 
that it should not have a wide distribution throughout the State. 
It is almost unknown for the interior of North and Northwest 
Missouri, and is perhaps best represented in numbers and typical 
form in the Osage basin. Its sub-species, pavonius Lea (which, 
at best, is perhaps only a color-variant) is not found in this State. 
The shell of this species is exceedingly variable, for this State, 
as to its shape, size and thickness, but these variations are only 
individual characteristics or deviations due to special local condi- 
tions. The author has found the breeding season of edentulus 
to be about as long and over-lapping as that of Lasmonos fragilis; 
however, there was a short interim noted in most individuals about 
the middle of July when there was more or less sterility. Because 
of the great vitality and nonparastic life of the larvae and also because 
of its constancy in breeding season, we might conclude the reasons 
for its prolificacy and wide geographic distribution; we might 
conclude, too, that its distribution may be due also to a dependent 
life as well upon fishes of those larvae that have been observed 
to escape from the extruded placentula, and, as some students 
have advanced, the buoyancy of the placentula, bearing the juve- 
niles, may be the greatest cause for the wide distribution. 
Sub-family Lampsilinae Ortmann. 
1911a—Lampsilinae Ortmann, An. Car. Mus., IV, pp. 337-338; 1912b, 
An. Car. Mus., VIII, pp. 300-360. 
ANIMAL CHARACTERS :—Mantle edge antero-ventrad to bran- 
chial opening of the female with special structures, such as papillae, 
flaps, etc., siphonal openings with tendency to become tubular; 
supra-anal separated from anal by a mantle connection of medium 
length; inner laminae of inner gills generally connected with 
the visceral mass throughout; palpi medium to small; mar- 
supium occupying only the outer gills, or parts of the latter, situated 
in their posterior portion as a rule; when sterile an extra thickness 
