THE NAUTILUS. 51 



and a peculiar formation of the sole, are among those Zonitidte which 

 are provided with a dart sack and dart, while Omphalina and 

 Hyalina (= Vitrea) are devoid of such. It is possible that the 

 formation of the foot may add features of distinction between various 

 natural groups of this complex family, and in close connection with 

 it may be the presence or absence of a caudal mucus gland (and 

 mucus pore). 



Systematic Review. 



ZONITID^E. 



Omphalina full 'ginosa Griff. Locomotive waves in a median zone 

 which is marked off by slight superficial lines, which are slight fur- 

 rows when the sole is detached from a surface. The waves are not 

 as distinct as, e. g., Polygyra, and apparently more remote from the 

 surface of the sole. 



Hyalina (Vitrea) indetitata Say and radiatula Aid. Waves in a 

 median zone, in the anterior or |, indistinct, and mostly not seen 

 at all near the posterior end. The surface layer undulating forward 

 and backward over [under] each advancing wave. 



Gastrodonta ligera Say. No waves seen. Foot and sole as de- 

 scribed above, for this and the four following species. A darkish 

 median line is ill-defined and has nothing to do with a locomotive disk. 



Zonitoides nitidus Mull., arboreus Say, minusculus Binn., Euconu- 

 lus chersinus Say. No waves ; no zones seen. 



L1MACIDJ2. 



Agriolimax campestris Binn. Waves in narrow median zone, 

 following each other in rapid succession, about ten simultaneously, 

 while the surface layer of the sole shows forward and backward un- 

 dulation with each wave. When the animal proceeds slowly (for a 

 snail!), the waves are more or less irregular, even undulating, and 

 sometimes no waves can be seen when the animal moves very slowly. 

 This has been noticed also on some other snails. 



CIRCINARIID^E. 



Circinaria concava Say. The waves extend over the whole width 

 of the sole ; the same was seen on a very small, young specimen ; 

 no zones seen. 



