THE NAIADES OF MISSOURI 353 
and thickened on edges of siphonal openings, white patch at base 
of branchial papillae, crenulated along border in front of branchial 
opening, post-ventral region of mantle darker than that of female; 
palpi united only at base, very long in old specimens; foot large, 
powerful, very extensile; gills dark tan, pointed posteriorly, inner 
gills longer and broader than outer, inner laminae of inner gills 
entirely connected to visceral mass. 
REPRODUCTIVE STRUCTURES:—Marsupia occupying posterior 
part of outer gill, reniform, consisting of about forty, leaf-like 
ovisacs and, when gravid, extending beyond original edge of gills, 
the extreme thickness of tissue here allowing the bulging out 
until glochidia escape through the ruptured edge; conglutinates 
white, elongate, leaf-shape, not very solid, usually surrounded with 
brick-red matter; glochidia among the very smallest (0.085mm. 
by 0:075mm.) belonging to the Lampsilis type (i. e., semi-elliptical, 
ventral margin rounded, gaping, hookless, short hinge line which 
is slightly undulate.) 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell medium in size, thin, alate, 
posterior end of female shell blunt; beaks compressed, marked 
with three or four wrinkles arranged in a double loop ending with 
two or three rather nodulous elevations at the base of the post- 
umbonal slope; epidermis straw color with bright green rays in 
young and well preserved specimens. 
INTERNAL STRUCTURE:—Cardinal teeth very weak, single in 
each valve; lateral teeth more solid, long, lamellar, elevated, no 
interdentum; muscle scars faint, retractor large and peculiarly 
placed; beak cavity shallow; nacre pearl-blue with the usual 
characteristic pink on the posterior portion. 
Sex Length Width Diameter Um. ra. Locality 
OO SOnex sea Omexe 22 NOM sOun( herches Cr Colima) 
GC 40 tex a 7On xe Ay o2n0 (Grande, Re, Utica) 
OF 7A, eX 1.30. xe 26 0.275 (Platte R., Agency Ford) 
OP FOR Sn 3p ask 2S 0.283 (102 R., St. Joseph) 
5 keene ke 5.5) (Os2008 (Osape cR=.iColley“s lord) 
BYSSIFEROUS JUVENILE:—The latter measurement is taken 
from a juvenile collected in the Osage River, Colley’s Ford Mo., 
July 15, 1913. It possessed a bysuss 160mm. long and was attached 
to a plicate shell. This byssal thread was so strong that it pulled 
off with some difficulty and was split in three strands near its 
