Occasional Papers of the Museum of Zoology 9 
The hinge-armature is similar to that of juvenile specimens, 
and the color of the nacre is that usual in medium-sized indi- 
viduals—i. e., lavender with copper tints. However, the shells 
are solid, somewhat inflated, and much eroded at the beaks, 
and have every external appearance of mature individuals. 
One (fig. 5) is quite sinuate on the ventral margin. They 
measure : 
Length Height-index Diameter-index 
Fig. 4 50 mm. 60 (30 mm.) 39 (19.5 mm.) 
Fig. 5 54 mm. 61 (33 mm.) 39 (21 mm.) 
Another 55.5 mm. 58 (32 mm.) 42 (23 mm.) 
E. plexus 55 64 44 (Simpson, 1914) 
U. pigerrimus 59 65 46 (C. and F., 1894) 
Unio coloratus has every appearance of a smooth specimen 
of this species. The question of U. plicatulus has already been 
discussed. U. pigerrimus easily falls within the range of varia- 
tion of this and the following form. 
The section Sphenonaias C. and F. (1894) Pe. U. lieb- 
mannt Ph.) is used here to include, besides the type, the more 
Elliptio-like forms of Psoronaias (type U. psoricus Morelet). 
The typical forms with higher umbones have much more the 
appearance of some of the southern species, placed by Simp- 
son (1914) in Quadrula, but which were also included in the 
section Psoronaias, as originally described. The section Bary- 
naias C. and F. (1894) is described in Part VII of the “Moll. 
terr. et fluv. de Mex.,” with U. pigerrimus as the single example, 
while in Part VIII that species is put under Psoronaias and 
U. sallei is listed as the sole example of the former section. 
Barynaias is thus a synonym of Psoronaias. Von Martens 
(1900) mistakenly calls U. sallei the type of Pachynaias C. 
and F. Barynaias is also a synonym of Sphenonaias, as used 
