32 THE NAUTILUS. 



undulatus, pustulosns, etc. In U. gibbosus the sexes may he rec- 

 ognized with a fair degree of probability by the more inflated shells 

 of the females. 



A decided difference we find in U. verrucosus Raf. (tuberculatus 

 Barn.), where the older females are considerably elongated at the 

 posterior end, that part of the shell being rather even, without the 

 characteristic undulations and warty prominences. In younger, 

 though fecund specimens, that feature is yet little marked. 



U. phaseolus shows no constant differences in the sutural shape of 

 the shell, but a decided one on the inner surface, in older speci- 

 mens. The female has, in each valve, a deep, oblique sulcus corre- 

 sponding with and leaving room for the gravid outer branchise. 



In the female Marg. marginata the posterior end is directed 

 downward and more inflated (with a stronger umbonal ridge), and 

 the same can be said of " An." edentula, although it is less marked. 



6. Numerical proportion of Sexes. In most species, the number of 

 males is in excess over that of the females, often considerably. A 

 few examples may be cited. Of 50 specimens of L. subrostratus 

 Say, from a lake in Indiana, only about one-third were females, and 

 the same must be said of a lot of L. nasutus from Ohio. Here, as 

 in many species, the females were averaging considerably smaller. 

 Of 115 U. pyramidatus, from the Ohio River, 71 were males, and 

 of eight retusus, seven were males, the eighth was young with the 

 gonad undeveloped. It is a question whether this be the normal 

 condition or due to local causes, or an evidence of beginning de- 

 generation. 



In concluding, it may be said that the time has come when new 

 species should be based not only upon the shells, but also the 

 soft parts, if such be obtainable. 



New Philadelphia, Ohio, April, 1898. 



A NEW UNIO. 



BY BERLIN H. WRIGHT. 



Unio villosus sp. nov. 



Shell ovate-elliptical, somewhat inflated, smooth, very inequi- 

 lateral, bluntly rounded or subbiangular behind, subtruncate before, 

 umbonal slope uniformly rounded above, disappearing at the lower 

 margin. Substance of the shell moderately thin; very slightly 



