194 THE AMERICAN MIDLAND NATURALIST 
the solidus of Lea and (in the conventional sense) may be called 
Pleu. solidum. The latter being antedated, we must use the 
former name. This species is rather typically represented in the 
Mississippi for Missouri, the mountain streams of South Missouri 
and also in the Neosho basin of South West Missouri. No real 
types are ever found in Central Missouri and not even forms are 
found in North Missouri. This species is distinguished from 
Pleu. coccineum by always being rather swollen and having a 
radial furrow more or less expressed. In this latter character 
it never reaches the extreme, as seen in obliqguum, of the pinched 
radial groove terminating in sulcus at the post-ventral margin. 
Its breeding record shows it to be tachytictic. 
Pleurobema coccineum (Conrad). 
(“Flat Nigger-Head,”’ ‘Pink Pig-toe,’”’ ‘‘Round Pig-toe.’’) 
Pl. TIT, Fig. Gob; Pl’ XX, Fig. 60 A and B. 
1836— Unio coccineus Conrad, Monog., III, p. 29, pl. XIII, fig. I. 
1900b—Quadrula coccinea Simpson, Proc. U. S. Nat. Mus., XXII, 
pp. 788-789. 
1912b—Pleurobema coccineum (Conrad) Ortmann, An. Car. Mus., 
VILL py 263: 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening densely set 
with papillae; anal with indistinct crenulations and papillae; 
mantle connection between. anal and supra-anal very close; gills 
wide, the inner wider and longer, inner laminae free from visceral 
mass; palpi long, united two-thirds of their length; color of soft 
parts tannish, mantle edge at siphonal openings black. 
REPRODUCTIVE STRUCTURES:—Only outer gills marsupial; 
when gravid marsupia swell moderately lengthwise in the center; 
conglutinates white, thin, leaf-shape, discharged whole; glochidia, 
suboval, spineless, medium in size measure 0.150 X 0.150mm. . 
SHELL CHARACTERS 
EXTERNAL STRUCTURES:—Shell subelliptical to subquadrate 
varying with age, flat, very much compressed through post half, 
greatly inflated (comparatively) anteriorly, dorsal and ventral 
margins curved about the same; beaks rather full not very well 
placed to the front, sculptured by concentric lines with two or 
