254 THE AMERICAN MIDLAND NATURALIST 
Arcidens confragosus (Say). 
(‘‘Black Pocket-Book,” ‘Black Pocket,” “Rock Shell,” 
‘Rock Pocket-Book.’’) 
PL. XXIL,, Fags..72: Avand ;B: 
1829—Alasmodonta confragosus Say, N. Harm. Dis., II, p. 339. 
1888— Margaritana confragosa B. H. Wright, Check List. 
1900b—A rcidens confragosus (Say) Simpson, Proc. U. §S. Nat. Mus. 
XXII, p. 662. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES :—Branchial opening large, with few 
papillae; anal with tiny papillae on inner edge; supra-anal very 
long, connected antero-dorsad two-thirds of length; inner gills 
somewhat wider, inner laminae free from visceral mass; color 
of gills and palpi brown, all other soft parts soiled white and chamois 
like. 
REPRODUCTIVE STRUCTURES:—Marsupium occupying only 
outer gills, light brown when sterile, spotted and vertically striated 
when gravid with early embryos, padiform and dark brown when 
gravid with ripe glochidia; internal structure of gravid marsu- 
pium typically Anodontine; glochidium of specimen from Platte 
River, Missouri, (0.355 x 0.350mm.) but possessing same shape, 
i. e., subtriangular, with undulate hinge line. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell subrhomboid, inflated, roughly 
sculptured with apiculated tubercles in umbonal region, ribbed 
tubercles on post-umbonal ridge, coarse undulations across post- 
ventrad part of disk, slopes of post-dorsal ridge sub-costated; 
beaks full, high, corrugated; epidermis brown to black in adult, 
greenish mingled with black in youth. 
INTERNAL STRUCTURES:—Cardinals single in right valve, 
double in left, the posterior one being long, serrated and placed 
just under the beak in place of the interdentum; laterals, faint in 
both vales; scars rather well impressed; umbonal cavity somewhat 
deep; nacre bluish to white with sky-blue border. 
Sex Length Width Diameter Um. ra Locality 
o '103 x .67 ex .48:.)mm“o.30 (Platte. Be Me) 
LOZ. JOSi kaw oun 0.34 (L. Contrary, Mo.) 
eS Min 7 Ae ee Sic n 0.31 (Osage R., Miss) 
ASR Bg Rk asigeee Stas Ci he i ) 
