Occasional Papers of the Museum of Zoology 7 



pansion is more developed than in the other specimens I have 

 seen. Figure I on plate II is of a specimen now in the Raven- 

 el collection, kindly forwarded to me by Mr. Mazyck, and 

 better represents the female shell as usually found. It meas- 

 ures : length 58, alt. 33, diam. 20 mm. It is very smooth and 

 of a waxy appearance (which seems to be quite characteristic 

 of the species), brownish-yellow with the rest-marks well in- 

 dicated, with indistinct, broad, green rays becoming deeper to- 

 words the posterior margin ; hinge very slight, much as in L. 

 lienosa (Con.). Inside of the left valve is written in Raven- 

 el's hand, "inodioliformis." 



The male shell has never been figured. Among the Ravenel 

 shell submitted to me by Mr. Mazyck was one, on the inside 

 of one of the valves of which Ravenel had written, "Distinct 

 from inodioliformis. Mr. Lea says it is uwdiolifonuis." 



This specimen (PI. II, figs. 2-3) agrees very exactly with 

 those in the Lea Collection and is unqeustionably the male of 

 the species. In Ravenel's time the sexual dimorphism in the 

 Naiades was not well understoo'd and without that apprecia- 

 tion the two forms are so difl^erent that Ravenel's opinion can 

 be easily understood. 



This shell is of a dark yellowish-brown, very indistinctly 

 rayed posteriorly ; smooth, but somewhat ridged along the rest- 

 marks ; the hinge is similar to that of the female. It measures : 

 length 53.5, alt. 27.5, diam. 19.5 mm. 



The shell figured on PI. II, fig. 5, was received by Lea from 

 Ravenel and by him given to Dr. Lewis and is now No. 15.753 

 Coll. Walker. It is apparently a female, but is more in- 

 flated than the Ravenel specimen (fig. i) and is much less ex- 

 panded posteriorly. In all other respects it is quite similar. It 

 measures : length 54, alt. 29, diam. 22.5 mm. 



Taking only the "valid" specimens into consideration, 



