350 THE AMERICAN MIDLAND NATURALIST 
genus is in its peculiar shell and glochidial characters. As to its 
animal characters it is essentially that of Obovaria and Amyg- 
dalonaias. Because of its spatulate and higher-than-long glocidia 
there is “‘a transition,’ as’ Dr. Ortmann aptly puts it, “toward 
the glochidia of the Proptera-ty pe,’ which has essentially the same 
hinge line and rounded ventral margin, but with different post- 
terior and anterior ends. 
Plagiola securis (Lea). 
(Butterfly.’’) 
Pl. II, Figs. 5a—6b. 
1829— Unio securis Lea, Tr. Am. Phil. Soc., III, p. 437, pl. XI, fig. 17. 
1834— Unto lineolata Say,t Am. Conch., VI. 
1g00b—Plagiola securis (ea) Simpson, Proc. U. S. Nat. Mus., XXII, * 
p. 603. x : 
ANIMAL CHARACTERS. 
NUTRITIVE CHARACTERS:—Branchial opening rather small 
with numerous papillae; anal crenulated; supra-anal very large 
closely, but definitely connected by mantle edges to anal; anus 
tentacled; inner laminae of inner gills free about three-fourths 
of their length from the visceral mass; palpi large, connected 
one-third of their length antero-dorsad; color of soft parts tan, 
or cream color with gills brownish and papillae yellowish. 
REPRODUCTIVE STRUCTURES:—Marsupium composed of about 
twenty-five ovisacs placed in the posterior half of outer gill; mantle 
border antero-ventrad to branchial opening with about fifteen 
very low, irregularly placed papillae; marsupium when charged 
with ripe glochidia color of brown sugar, somewhat kidney shaped; 
conglutinates not very solid; glochidia subelliptic or spatulate 
hinge line very short, ventral margin round, spineless, much higher 
than long (0.230 x .330mm). 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell sub-triangular, not very much 
inflated, compressed in umbonal region, truncated narrowly post- 
dorsad; disk more or less smooth; beaks somewhat pointed 
and directed anteriorly, sculptured with a few fine concentric 
‘This name, as employed by Say, was really preoccupied by Rafinesque 
in his Monograph of 1820 and hence through priority this species should 
bear the name Plagiola lineolata (Raf.) in spite of the fact that Simpson 
considered this as one of the many ‘‘indeterminates’’ of Rafinesque. 
