THE NAIADES OF MISSOURi 153 



and thickened on edges of siphonal openings, white patch at base 

 oi branchial papillae, crenulated along border in front of branchial 

 opening, post-ventral region of mantle darker than that of female; 

 palpi united only at base, very long in old specimens; foot large, 

 powerful, very extensile; gills dark tan, pointed posteriorly, inner 

 gills longer and broader than outer, inner laminae of inner gills 

 entirely connected to visceral mass. 



Reproductive Structures: — Marsupia occupying posterior 

 part of outer gill, reniform, consisting of about forty, leaf-like 

 ovisacs and, when gravid, extending beyond original edge of gills, 

 the extreme thickness of tissue here allowing the bulging out 

 until glochidia escape through the ruptured edge; conglutinates 

 white, elongate, leaf-shape, not very solid, usually surrounded with 

 brick-red matter; glochidia among the very smallest (0.085mm. 

 by 0.075mm.) belonging to the Lampsilis type (i. e., semi-elliptical, 

 ventral margin rounded, gaping, bookless, short hinge line which 

 is slightly undulate.) 



SHELL characters. 



External Structures: — Shell medium in size, thin, alate, 

 posterior end of female shell blunt; beaks compressed, marked 

 with three or four wrinkles arranged in a double loop ending with 

 two or three rather nodulous elevations at the base of the post- 

 umbonal slope; epidermis straw color with bright green rays in 

 young and well preserved specimens. 



Internal Structure: — Cardinal teeth very weak, single in 

 each valve; lateral teeth more solid, long, lamellar, elevated, no 

 interdentum; muscle scars faint, retractor large and peculiarly 

 placed; beak cavity shallow; nacre pearl-blue with the usual 

 characteristic pink on the posterior portion. 



Sex Length Width Diameter Um. ra. Locality 



(Perche Cr., Columbia) 

 (Grande R., Utica) 

 (Platte R., Agency Ford) 

 (102 R., St. Joseph) 

 (Osage R., Colley's Ford) 



ByssiFEROUS Juvenile: — The latter measurement is taken 

 from a juvenile collected in the Osage River, Colley's Ford Mo.. 

 July 15, 1913. It possessed a bysuss i6omm. long and was attached 



