THE NAUTILUS. 127 



SUPERFAMILY GnATHOPHORA. 



Jaw present. 



I. Orifices of genitalia contiguous or united Monotremata. 



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

 ing the whole upper surface Ditremata. 



The Monotremata divide naturally into two divisions: 



1. Lateral teeth of the aculeate or thorn-shaped tyi)e Vitrinea. 



2. Lateral teeth of the quadrate type Helicea 



1. Families of Vitrinea. 

 a. All of the teeth aculeate Selenitida'. 



h. Central and lateral teeth quadrate, uncini aculeate Liniacldce 



SelenitidvE. 

 This family is not very distinct from Limacidte, 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. 



Lhnacidce. 

 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 presence or absence of a caudal 

 mucus gland is equally unreliable, for genera otherwise closely 

 allied, vary in this character. 



The additions to our Limax list being unimportant will be 

 <leferred. 



Additional species of Zonites. 

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

 Z. Simpsoni Pilsbry. Indian Territory. 



A NEW SPECIES OF ARCONAIA. 



HY H. A. PII.SRRY. 



TJnio (Arconaia) Provancheriana •'p. nov. 



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

 twisted, very strongly resembling Area (Parallelopipedtim) tortuosa 

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

 Anterior and posterior margins rounded ; basal margin gently 



