THE NAUTILUS. 127 



SUPEKFAMIIA' GnATHOPIIORA. 



Jaw })resent. 



I. Orifices of genitalia contiguous or united Monotremata. 



II. Orifices of genitalia widely sejiarated ; no shell; mantle cover- 

 ing the whole upper surface iJitremata. 



The Monotremata divide naturally into two divisions : 



1. Lateral teeth of the aculeate or thorn-shaped type Vitrinea. 



2. Lateral teeth of the quadrate type Helicea 



1. Families of Vitrinea. 

 a. All of the teeth aculeate Selenitidce. 



I). Central and lateral teeth quadrate, uncini aculeate Linuicalce 



Selenitidce. 

 This family is not very distinct from Limacid?e, but the radula 

 is more highly specialized. Of the genus Selenites numerous varie- 

 ties and forms have been described since the publication of my 

 check-list. They will be enumerated later. 



Limacidce. 

 All attempts to split this group into two or more families have 

 proved impracticable. The various genera exhibit every stage in 

 the degeneration of the shell. The pi-esence or absence of a caudal 

 mucus gland is equally unreliable, for genera otherwise closely 

 allied, vary in this character. 



The additions to our Li)na.v list being unimportant will be 

 deferred. 



Additional species of Zonites. 

 Z. Shimekii Pilsbry. Loess formation of Iowa and Nebraska. 

 Z. Simpsoni Pilsbry. Indian Territory. 



A NEW SPECIES OF ARCONAIA. 



BY H. A. PILSKRY. 



TJnio (Arconaia) Provanclieriaiia sp. nov. 



Shell wide, oblong, beaks at the anterior third. The whole shell 

 twisted, very strongly resembling Area (Parallelopipeduni) tortuosa 

 L., in the direction and degree of the twist. Hinge-line sigmoid. 

 Anterior and posterior margins rounded; basal margin gently 



