NAIADES OF MISSOURI 69 



septa closely crowded, when charged distended very little even in 

 median-longitudinal line, ventral edge not blunt, ovisacs rather 

 narrow; conglutinates white, narrowly lanceolate, not solid; 



glochidia large, spineless, ventral margin rounded, hinge line short, 

 straight, or nearly so, measures 0.26"/ x o.j2jmni., collected by author, 

 Aug. II, 1913, Osage River, Bagnell, Missouri. 



SHELL CHARACTERS. 



External Structures: — Shell oval quadrate, medium in 

 size, compressed, heavy, thick, rounded in front, usually emargi- 

 nated post-dorsad with radial furrow from this sulcation to beaks, 

 dorsal ridge rather high with upcurved costae; post-umbonal 

 ridge rather rounded; posterior half of shell profusely sculptured 

 with coarse pustules and fine tubercles; umbones low, pitched 

 considerable anteriorly, sculptured with numerous, heavy, wavy 

 or corrugated ridges which extend down on upper part of disk; 

 epidermis brownish red to black. 



Internal Structures: — Cardinals double in left, rather 

 tripartite in right valve; laterals double in both valves, lower 

 right lateral rudimentary, scars deep; beak cavities very deep 

 antero-postero, narrow diametrically, wide vertically, nacre 

 rich purple, with part within the mantle line a lighter shade, 

 sometimes whole nacreous surface faded to whitish with pinkish 

 teeth. 



Sex Length Height Diameter U. ra. Locality. 



9 80 X 60 X 37mm 0.120 (Meramec R., Fern Glen) 

 cf 64 X 54 X 27 " 0.135 (Gasconade R., Gascondy) 

 9 63 X 62 X 33 " 0.128 (Osage R., Schell City) 



The last measurement is that of the smallest juvenile out of 

 a collection of 156 collected in a space twenty-feet square in the 

 White River. This place was a quiet retreat of shallow water with 

 a thin doating of mud over a substratum of limestone. 



Miscellaneous Remarks: — The peculiar shell characters 

 of this species in being suborbicular, heavy, with low corrugated 

 beaks and the unique anatomical characters in possessing no 

 supra-anal opening and only outer gills as marsupial are features 

 especially to be noted. Its distribution in this state is peculiar 

 in that it is not found at all in the interior northern drainage of 

 the Mississippi River, and is confined in its typical form more in 

 the drainage of the south slope of the Ozarks and in the Missouri 

 portion of the Mississippi while it occurs by intergrades in the 



