THE NAUTILUS. 63 



varying from pale strawcolor to blackish brown ; anterior slope 

 longer than the posterior, rather conspicuously compressed and 

 attenuate, with no circumscribed lunule ; posterior slope flat- 

 tened, externally bordered by a sharp angle surmounted, as in 

 M. alata, by an elevated thin keel ; the inner margins pout a 

 little near the beaks, the middle of the flattened space has in 

 each valve a single conspicuous rib ; the cordate space between 

 these ribs are somewhat concave ; the spaces between the ribs 

 and the keels are flat and from the distal ends of the ribs to 

 these of the keels the valve margin show a wide lanceolate gap ; 

 there is also a narrow anterior basal gap ; the hinge is normal ; 

 the surface of the valve smooth except for lines of growth ; the 

 pallial sinus short and angular ; the basal margin prominently 

 arcuate and the middle of the shell inflated. Length 78, height 

 66, diameter 34 mm. 



There is a constriction in front of the keel which varies in 

 strength in different specimens. The shell is divided from M. 

 exoleta by the presence of the keel, the latter possessing only an 

 angle ; it differs from M. alata in its exaggerated arcuation, 

 much higher beaks and anterior attenuation. 



STUDIES IN NAJADES. 



BY A. E. ORTMANN. 



(Continued from page 143, Vol. 28. ) 

 EURYNIA (MICROMYA) PERPURPUREA (Lea) (See Lampsilis perp. 



Simpson, 1900, p. 558). 



I collected, on Sept. 20, 1912, a number of males in Clinch 

 River, at Richland, Tazewell Co., Va., and on Sept. 21, 1912, 

 a single gravid female, with glochidia, at Raven, Tazewell Co., 

 Va. 



Anal separated from the supraanal by a rather short mantle 

 connection, which is shorter than the anal. Inner edge of anal 

 with very distinct crenulations. Branchial with papillae. In 

 front of the branchical, the female has about 10 subcylindrica 

 or subconical papillae of medium size, which are rather distant 

 from each other, and of slightly variable size, and do not extend 



