X EXTERNAL ANATOMY. 



EXTERNAL FEATURES OF ANIMAL. 



The general form of the animal in Helicidce is similar to that of 

 Zonitidce, etc. The shell is carried on the middle or somewhat 

 behind the middle, its axis being held oblique or vertical to the 

 plane of the sole. The head has the usual eye-peduncles and ten- 

 tacles, and more or less distinct labial lobes (see frontispiece, fig. 7). 

 The mantle rarely projects beyond the lip-edge of the shell, and is 

 generally provided with right and left body lobes (frontispiece, fig. 

 7, r.L right lobe, LI. left lobe). Sometimes the latter emits one or 

 two small tongue-like processes on the left side (pi. 33, fig. 7). The 

 back, from mantle to head, generally shows one or several dorsal 

 grooves. The sides are granulated in various patterns, and often a 

 groove extends from the lips obliquely upward to mantle on each 

 side, the facial grooves (see pi. 33, figs. 7, 8 ; frontispiece, fig. 7). 

 The tail in some genera has a median longitudinal groove (espe- 

 cially in Epiphallocjona) or sometimes a serrate keel (Lysinoe, Oxy- 

 chonci). Usually, however, it is rounded above and shows no special 

 features, being granulated like the sides, but more finely. In the 

 Endodontidce and Zonitidce a deep longitudinal furrow runs parallel 

 to the foot-edge on each side a short distance above it. These are 

 the parapodial or pedal grooves (see pi. 14, fig. 46). They are 

 absent in Helicidce. In Zonitidce and findodontidce these furrows are 

 often associated with a mucus-secreting pore at the tail. The sole or 

 creeping disc is divided longitudinally into three bands or areas in 

 some genera, but in most Helices such division is absent, or indica- 

 ted by coloring only. 



DIGESTIVE TRACT. 



The jaw is well developed and usually strong and orange-colored 

 in Helices. The types of jaw occurring in Helicidce, Endodontidcer 

 and Zonitidce are 



Polyplacognath (or unsoldered type of jaw, see pi. 1, figs. 4, 5, 6 r . 

 9) consisting of numerous separate plates, overlapping at their edges, 

 JUH! united by a common membrane only (Punctum). 



Stegognath (or plaited, pi. 15, fig. 6, 7) composed of similar or 

 narrower vertical plates soldered together, but with free, overlapping: 

 outer edges (F/mninn/!.na, tiagda). 



Ooniognath (or converging-plaited, pi. 42, fig. 36) same as stego- 

 gnathous type, but outer imbricating edges of each plate converg- 



