THE NAIADES OF MISSOURI I 75 



row of papillae on the inner edge extending down quite to the 

 central part of the ventral edge. These papillae are often quite 

 tentacular and are rather regular and uniform in shape and size 

 and are never widely separated as in case of the Micromya mantle 

 edge of this anterior branchial border. Its inner laminae of the 

 inner gills are usually entirely connected with the visceral mass; 

 however, a small hole is sometimes left at the posterior end post- 

 dorsad to foot. 



Shell Characters: — In shell characters there are no great 

 distinctions to be considered as a group since the chief distinguish- 

 ing characteristic is in the post-mantle edge as above discussed. 

 Its beak sculpturing is identical with that of the Micromya shell 

 being sinuated or double-looped, the posterior loops being more 

 or less broken behind. 



This group of Eurynia is represented in this State by E. (E) 

 suhrostrata and rccia, both having rather wide distribution. 



Eurynia (Eurynia) subrostrata (Say). 



("Common Pond- Mussel," "Lilliputian.") 



PI. XXVII; Figs. 101 A—D. 



1 83 1 — Unio subrostratiis »Say, New Harm. Dips. 



1850 — Unio mississippiensis Conrad, Jl. Ac. N. Sci. Phila., i, p. 277, 



pi. XXXVIII, fig. u. 

 1868 — Unio topekensis Lea, Pr. Acad. Nat. Sci. Phila., XII, p. 144. 

 1900b — Lavipsilis sitbrostratiis Simpson, Pr. U. S. Nat. Mus., XXII, 



P- 546. 

 1912b — Eurytiia (Eurynia) subrostrata (Say), Ortinann, An. Car. Mus., 



VIII, p. 344- 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening narrowly papil- 

 lose; anal finely papillo.se supra-anal separated from anal by a 

 rather short mantle connection; inner laminae of inner gills con- 

 nected to visceral mass; palpi rather small and connected antero- 

 dorsad about one-fourth of its length; color of soft parts grayish 

 with mantle edge along siphonal region blackish. 



Reproductive Structures: — Marsupia kidney (or rather) 

 fan-shaped, consisting of twenty large, well defined ovisacs, dis- 

 tended, when gravid, at ventral edge thus giving the congluti- 

 nates a club-like shape; ventral tips of ovisacs beaded bearing 

 bluish pigment with glochidia scattered throughout the sacs; 



