THE NAIADES OF MISSOURI 443 
REPRODUCTIVE STRUCTURES:—Marsupium rather reniform 
occupying over posterior half of outer gills and consisting of sixty- 
fivé ovisacs well separated, when gravid extending below original 
ventral edge of sterile marsupia; inner mantle edge antero-ventrad 
to branchial opening a specialized flap reaching down to lowest 
point of the post-ventral part of shell where it is developed into a 
tentacular lobe; conglutinates white, sole-shaped, not very solid, 
glochidia medium in size, sub-elliptical, spineless, hinge line rather 
short, evenly curved, measuring 0.185 x 0.210 mm. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell elongate-elliptic, medium in 
size, subsolid, disk smooth; umbones large, but not full, sculpture 
by five or six double looped or sickle-shaped ridges most pronounced 
and opened at base of post-umbonal slope; epidermis straw-color 
(usually without much display of rays) smooth, polished; female 
shell much produced at the post-ventral edge of shell and continued 
upward as a marsupiual inflation for a short distance; male shell 
pointed posteriorly. 
INTERNAL STRUCTURES :—Cardinals prominent, serrate, double 
in right valve, single in left; beak and branchial cavities rather 
deep and basin-like; nacre satin-white, irridescent posteriorly. 
Sex Length Height Diameter Locality 
& 120 x 60 x 45mm—(Chariton R., Kern) 
Q@ 100 x 50 x 38mm—(Miss. R., Hannibal) 
50 x 23 x 16mm—(Grand R., Darlington) 
P25 x0 OF Xo) eSttim——(Grand Re, Utica) 
The last measurement was that of one of the smallest juveniles 
obtained by the writer. It has a black border to its shell and a 
short byssus extending from between the valves at ventral portion 
of shell. 
MicELLANEOUS REMARKS:— Even in the juvenile anodon- 
toides there is some difference from that of the fallaciosa shell 
in that there are not as evident. The main distinction between 
the adult shells of these two species is that of fallaciosa is bril- 
liantly rayed, is smaller, has more reddish beaks and is a dweller 
in muddy creeks, sloughs and lakes while anodontoides loves sandy 
situations of swifter water and develops a large, thick shell, rayless, 
-unicolored epidermis and is a most active mussel. When perfect 
(as it is found in the Chariton and Mississippi Rivers) it is one of 
