THE NAIADES OF MISSOURI 1 25 



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 itg 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 jragilis; 

 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 



