52 THE NAUTILUS. 



HELICID^. 



Polygyra hirsuta,fraterna, tridentata, fraudulenta, injlecta, palliata, 

 mitchelliana, thyroides, albolabris and var. minor, profunda : waves 

 very distinct, in a rather sharply defined median zone, regularly 

 proceeding from the posterior end to the anterior, about 7 or 8 

 simultaneously in hirsuta and fraterna, 10 to 12 in the large species. 

 Marginal zones with fine radiating lines. 



It may be noted here, in a general way, that the number of waves 

 is easily over-estimated, and it is somewhat difficult to count them, 

 if more than two to four. 



Helix ( Tachea) hortensis Miill. Zones plainly visible ! the mar- 

 ginal areas rather narrow; waves, in the median, distinct. 



Vallonia pulcheUa, excentrica, costata : no zones seen ; waves 

 extending over the whole width of the sole, rather fast, about four 

 simultaneously. The waves can be seen in lateral view, in trans- 

 mitted light. 



Note. — There is a possibility, however, that in these and other 

 minute snails, narrow marginal zones exist and have been over- 

 looked, to which the waves are transmitted. 



ENDODONTID^. 



Patula solitaria, alternata, perspectiva, striatella, Helicodiscus 

 lineatus Say : no zones seen, and no waves. It seems that the for- 

 mation and texture of the sole are rather different from those of 

 Polygyra, and more like those of Gastrodonta and Zonitoides. 



PHILOMTCID^. 



Philomycus caroliiiensis Bosc, and another species which is prob- 

 ably distinct : no zones, and no waves seen. 



PCPID^. 



Bifidaria armifera Say. No zones seen ; waves extending over 

 the whole width of the sole, about four simultaneously, rather irreg- 

 ular, and often disappearing before reaching the anterior end, and 

 apparently commencing anywhere, also stopping and quasi rebound- 

 ing anywhere ; in short, more irregular than in any other species. 

 This seems to be concordant with the jerky motion of the animal. 



Vertigo ovata Say. Sole with three zones, the median one widen- 



