NAIADES OF MISSOURI 107 
and more typical shell of the main species. This subspecies, 
however, is more like the type than the trzgonoides of Frierson, 
the latter being more nearly the flava type and hence might be 
well named ‘“‘F. undata flava (Raf.)”’ 
Fusconaia undata trigonoides Frierson, MS. 
(* Big -Pigtoe.’*) 
PEERY — Pigs. go A) PV Fags. Oa;and ob- 
1913—Fusconaia undata trigonoides Frierson MS.—Personal Letter, 
February 22, 1913. 
ANIMAL CHARACTER:—Soft parts indentical with species. 
Glochidium measures 0.180 x 0.165mm; conglutinates white in 
glochidial and late embroyonic stages, pink in earlier stages. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:— Shell elongate trigonal, thick, 
heavy, very large for the genus; disk without sculpturing except 
that rest-lines are somewhat furrowed giving an undulate appear- 
ance to growth lines; beaks comparatively low and not placed 
so much anteriorly, sculptured with concentric bars breaking into 
two or three nodules at base of post-umbonal ridge; post-dorsal 
part of shell, bowed, slightly biangulated behind; epidermis 
cloth-like, reddish brown to horse bay color, rayed in young. 
INTERNAL STRUCTURES:—Identical with those of the species 
and other intergrading forms, except that it may vary from a 
white to pink nacre. 
Length Width Diameter Location 
G37 OG, XA (Platte R., Dixon Falls, Mo.) 
7OMEX ESO) 6°35 (Osage R., Schell City, Mo.) 
FO exe AO 2X 24. (Osage R., Warsaw, Mo.) 
2 ee? OEE LA) (Platte R., Garretsburg, Mo.) 
The juvenile indicated by the measurement under the last 
number was found lying on its side in the shallow water of a riffle. 
It is different from the mature shell in its dark yellow epidermis 
marked all over by green rays, also by more prominent umbonal 
‘ridge, more centrally placed and more distinctly sculptured beaks. 
The soft parts are all of a bright orange color except the bluish 
visceral mass. 
This specimen and also the one under the first measurement 
of the above list were kindly indentified by Dr. Ortmann as F: 
