THE NAIADES OF MISSOURI . 341 
‘except N. ellipsi formis when the former is young. However, the 
more elliptic shell with broader, straighter rays would serve as 
the main distinguishing features. Surber (1913, p. 109) has found 
that its glochidium is a gill parasite upon the white bass (i. ° 
chrysops) as a natural host. Breeding records have been care- 
fully kept for this species, especially for commercial reasons, to 
find that it is typically bradytictic. 
Nephronaias ligamentina gibba (Simpson). 
1900b—Lampsilis ligamentinus gibbus Simpson, Proc. U. S. Nat. Mus., 
XXII,p. 540. 
(“Southern Mucket,”’ “Yellow Mucket.’’) 
ANIMAL CHARACTERS:—Identical with those of the parent 
species, except, of course, in short gills and other modified parts 
due to a shorter shell. The glochidia are the same. 
SHELL CHARACTERS:—Shell “peculiarly short, humped form”’ 
(Simpson); thicker, heavier more inflated with more roughened 
growth lines and more of a yellowish epidermis than the parent 
shell. 
Sex Length Height Diameter Locality 
Sosa Sen OO, X&) AO: (Osage R., Monegaw Springs) 
OF 8002s 164 <x vAomim (a3 ” Linn Creek) 
” ” 
BSG) 2 7O. (1 3omm ( Bagnell) 
MISCELLANEOUS REMARKS:—Gibba seems to be a rather 
common variety throughout the southern range of the species 
and is expecially characterized by the short, stout, “humped” 
form of shell. Perhaps it bears the same relation to its species as 
dakotana Frierson does to grandis Say. ‘The writer’s experience 
in the study of the form of lxgamentina while on a 300-mile float 
down the Osage was that it was difficult to ascertain the point 
of separation between the species and the variety, gibba, so imper- 
ceptibly do they grade into each other. This form is met with in 
drainage of the Ozark Center as well—especially in' the Black 
River. 
Nephronaias ellipsiformis (Conrad). 
(‘‘ Ellipse.”’) 
Pl AON Vij. Ves. 60, AD). 
1836— Unio ellipsiformis Conrad, Monog. VIII, p. 60, pl. XXXIV, fig. TI. 
1845— Unio spatulatus Lea, Proc. Am. Phil. Soc., IV, p. 164. 
1898—Lampsilis spatulatus oo Molle" Chicaco,, Pts: p. 106, 7p! 
Pee fie. 5°) pl.) ITT, fig to: 
