394 THE AMERICAN MIDLAND NATURALIST 
intact as a saddle over the beginning of its adult shell. No species, 
perhaps, has such tubular development of mantle edges for the 
branchial and anal openings. In this state its distribution is 
peculiar, being almost exclusively found in North Missouri and 
never in South Missouri. It is often found in company with 
alata from which it can be separated on account of thick shell and 
coarser epidermis of the latter. It may be mentioned here that 
laevissima shows the highest modern development of the siphonal 
openings, 1. e., into the actual tubular form. (See Plate IX). This 
Species is distinctly bradytictic. 
Proptera capax (Green). 
(‘“Pocket Book,” ‘‘Swell.Shell.’’) 
PIUXXV ES Fess 03° A and’ e: 
1832— Unio capax Green, Cab. Nat. Hist., II, p. 290. 
1899—Lampsilis capax Smith, Bull U.S. Fish Com., p. 291, pl. LX XIV. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening with rusty red 
papillae arranged in two ranks; anal finely crenulated; supra-anal 
large with two large tentacular structures on each mantle edge; inner 
laminae of inner gills entirely connected; palpi rounded antero- 
ventrad, connected antero-dorsad two-thirds of their length; 
color of soft parts tanish, mantle edge antero-ventrad, reddish- 
brown. 
REPRODUCTIVE STRUCTURES:—Marsupium occupying the 
greater posterior part of the outer gill, consisting of about fifty 
small ovisacs distended transversely when gravid, and being also 
distended at the distal ends the ovisacs presenting teat-like 
appearance; no mantle flap antero-ventrad to branchial opening, 
nor any specialization except for a thickening of the mantle edge; 
conglutinates not solid, white; glochidium ax-head or hatchet- 
shape in form, spined, rather small, 0.105 x 0.185mm. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell rather globose, extremely 
inflated; disk smooth; beaks extremely full, round, high, sculp- 
tured with single tubercles on incurved tips surrounded by fine 
concentric ridges looped into two or three small tubercular mark- 
ings at very base of post ridgé; epidermis smooth, polished, 
