258 THE AMERICAN MIDLAND NATURALIST 
but glochidia are held together in loose masses by brownish mucus ~ 
and coiled larval threads. 
Fic. 7. Mature closed glochidium of L. suborbiculata. (x87.) 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell subround, or suborbicular, 
thin, compressed, rounded before, bowed ventrad, pointed behind, 
sulcated post-dorsad, alated, dorsal line from apex of wing to an- 
terior end, straight and at an angle of 45 degrees; disk smooth; 
beaks flattened, sculptured with coarse wavy bars, intermediate 
ones bow-shaped and arched toward apex, latter double-apiculated 
with smaller tubercles just ventrad, later bars subundulate on 
upper disk and running more or less parallel with growth lines; 
epidermis polished, straw colored in young. light brown-born in 
old; rayed all. over with green capillary lines and one or two 
broad bluish-green bands from beak to extreme posterior point 
of shell; growth lines raised and undulated showing through on 
nacreous surface. 
INTERNAL STRUCTURES:—Cardinals and laterals entirely 
lacking; anterior adductor muscle scars two comparatively deep 
elongated triangular areas, progressive impressions most distinct; 
other cicatrices very faint, confluent, mantle line broken by 
minute ridges; umbonal cavity shallow; nacre whitish, bluish 
or coppery, irridescent. 
Sex Length With Diameter Um. ra. Locality 
9 185 x 130 x 67mm _ 0.290 (Lower LL. Contrary, St. Joseph) 
Ser SOV Pki try x AON. o270,) (Uppers. Contrary, eS 
PRA BiX5 48 SEX me ee 0.260 (Sugar Lake, Armour, Mo.) 
SA Bw Rin 2Sir SSP One 0.250 (lL. Contrary, St. Joseph, Mo.) 
The latter measurement is that of the smallest juvenile of 
this species out of a collection of a little over a hundred of these 
delicate shells. This one was without byssi and doubt is expressed 
