1 62 THE NAIADES OF MISSOURI 



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 shoivs the highest modern development of the siphonal 

 openings, i. e., into the actual tubular J or m. (See Plate IX). This 

 Species is distinctly bradytictic. 



Proptera capax (Green). 



("Pocket Book," "Swell Shell.") 



PI. XXVI, Figs. 93 A and B. 



1832 — Utiio capax Green, Cab. Nat. Hist., II, p. 290. 



1899 — Lampsilis capax Smith, Bull U. S. Fish Com., p. 291, pi. LXXIV. 



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 o.iSsmm. 



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 ridge; epidermis smooth, polished, 



