10 HELIX. 



Group II. LEUCOCHROA, Beck, 1837. 



Shell imperforate to moderately umbilicated, globose or de- 

 pressly globose, thick, white, or dull-colored, cretaceous ; whorls 

 about five, usually with more or less angulated periphery, the 

 last slightly descending in front; peristome simple, thickened, 

 columella callously dilated, often covering the umbilicus. Jaw 

 oxygnathous. Cir cum- Mediterranean Region. H. CANDIDISSIMA, 

 Drap. 



The sj-nonyms are Calcarina, Moquin-Tandon, 1845, and 

 Iberus (in part), H. and A. Adams, 1855. 



Section LEUCOCHROA (sensu stricto). 



Aperture broadly lunar, rounded, often with a small outer 

 angle, corresponding with the peripheral carina. 



Section MIMA, Westerlund, 1866. 



Aperture very angular, much thickened within, especially 

 above, where it develops two strong tubercles or tooth-like pro- 

 jections subconfluent into one, narrowing the mouth. 



On account of the ribless jaw of H. candidissima, and for 

 other peculiarities, Dr. von Martens classed this group with the 

 Zonitidse. The investigations of Binney have shown that H. 

 Boissieri, also a Leucochroa, has a ribbed jaw and the dentition 

 of Helix. The heavy shells, and absence of a mucous pore are 

 characters which serve to confirm the classification here adopted. 



(Section LEUCOCHROA, sensu stricto.) 

 H. CANDIDISSIMA, Drap. PI. 2, figs. 31-35. 



Subimperforate, globose, solid, cretaceous ; whorls 5, rather 

 flattened, the upper ones carinate above the suture, carina after- 

 wards becoming evanescent, the last deflected in front ; peris- 

 tome subpatulous, thickened within. Diam. 16-25 mill. 



Southern France, Italy, Algiers. 

 Var. RIMOSA, Jan. Fig. 34. 



Subcarinate, umbilicus rimose. Diam. 20 mill. 

 H. depressa, Miihlf., is a synonym. 



Yar. HIEROCHUNTINA, Boissieri. Fig. 35. 



