HELICODONTA. 285- 



26, 27 (see also pi. 56, figs. 16, 17, H. constrida ; figs. 18, 19, H. 

 lens; figs. 23, 24, H. triaria ; figs. 28, 29, 30, H. biconcava; figs. 31, 

 32, 33, H. nautiliformis). 



Animal rather elongated, with long, narrow foot, the sole undi- 

 vided ; back with a pair of longitudinal grooves ; facial grooves 

 wanting. Mantle with a small right body-lappet; no left one. 

 Right eye-retractor passing between branches of genital system. 

 Epiphragm papery, flat, formed rather deep in the mouth. 



Jaw thin and flexible, with numerous (6 to 16) broad, flat ribs r 

 separated by narrow interstices (pi. 36, fig. 6, H. lenticula; pi. 36, 

 fig. 8, H. maroccana). 



Radula having the mesocones slightly longer than the basal 

 plates, ectocones small. Marginal teeth having the ento- and meso- 

 cones united at base, ectocone developed (pi. 36, fig. 5, H. lenticula. 

 PI. 36, fig. 7, H. maroccana). 



Genital system: penis long, the retractor median or terminal, 

 inserted didally on columellar muscle; no flagellum. Vagina long, 

 bearing from one to three cylindrical elongated mucus glands, with 

 one dart sack at or below their base, sometimes lacking ; the dart, 

 when present, short and conical (pi. 36, fig. 9, H. lusitanica^. 

 Spermatheca oval, its duct short, bound to the uterus and without 

 diverticulum. See pi. 36, fig. 4, H. obvoluta; pi. 36, fig. 10, if. 

 lusitanica. 



The number of mucus glands varies from one to three. H. obvo- 

 luta has one long and one very short gland. The dart sack is en- 

 tirely absent in some species. The dentition is of the type usually 

 developed in ground snails. The jaw is uncommonly delicate for 

 the ribbed type. The union of the penis retractor muscle with the 

 great columellar retractor is a peculiar feature, and it will be inter- 

 esting to find whether it holds throughout the genus. I have ob- 

 served it in H. obvoluta only. 



The brownish, unicolored shell, with depressed spire, slowly 

 widening narrow whorls and reflexed, lipped peristome, is very 

 characteristic ; and no shells of the Palsearctic fauna, except Isog- 

 nomostoma and Dibothrion can be compared with this genus these 

 two groups also having toothed apertures, but sufficiently different 

 in form from those jf Helicodonta. 



Von Ihering maintains, I believe with right, that this genus is 

 more nearly allied to Fruticicola than to Helix or Campylcea, differ- 



