1 68 tHE NAIADES OP MISSOURI 



Animal Characters: — Siphonal openings well formed; 

 inner laminae of inner gills usually entirely connected to the 

 visceral mass; in male no specialization, but in female the inner 

 edge of mantle antero-ventrad to branchial opening always with 

 well developed papillae, or short tentacles which often extend to 

 the central of ventral edge; marsupium reniform, swollen, con- 

 sisting of many ovisacs occupying posterior part of outer gill 

 and ventral edges beaded in white or black pigment when gravid; 

 conglutinates white, not very solid; glochidia 'large or medium 

 in size, semi-elliptical. 



Miscellaneous Remarks: — The special structures on the 

 mantle antero-ventrad to the branchial opening would group 

 this genus among the highest of the Lampsilinae from the fact 

 that the aeration of the embryos is well secured through such 

 specialization. Especially because of the number, form and 

 arrangement of the papillae two sub-genera may be marked out. 

 In the following description when the specialized mantle edge is 

 discussed the female is considered. 



Sub-genus Micromya Agassiz. 



(Type, Unio jahalis Lea.) 



1852 — Micromya Agassiz, Arch, fiir Nat., p. 57; 1912b, Ortmann, 

 An. Car. Mus., VIII, p. 337. 



Animal Characters: — Mantle edge antero-ventrad to bran- 

 chial opening specialized by papillae, both regular and irregular, 

 arranged rather widely separated in a single row but never 

 extending to the middle of the ventral margin; inner laminae of 

 inner gills entirely connected, or more or less free. 



Shell Characters: — Shell sub-elliptical, small or medium in 

 size ; beak sculpture rather double' looped-or distinctly sinuate 

 with the posterior sinuation rather open. 



Miscellaneous Remarks: — This sub-genus is represented 

 in this state by three species — all found only in the Ozarks. 

 The type Jahalis of Lea of Micromya is not found anywhere in 

 Missouri. The essentia) distinction between the two sub-genera, 

 Micromya and Eiirynia (sens, strict.) is in the less extensive and 

 less crowded arrangement of the papillae on the inner edge of the 

 mantle antero-ventrad to branchial opening in the former. 



