HYGROMIA. 269" 



Genus HYGROMIA Risso, 1826. 



=Hygromia Risso, 1826,+ Brady bcena Beck, 1837 (part),-f jFVw- 

 tidcola Held, 1837,-J-ifonac/iaFitz., 1833,-j-THc/imHartm., 1841?' 

 +Petasia Beck, lS37,+Metodonta Mlldff., 1886, etc., etc. 



Shell rather thin and subtranslucent, with little calcareous sub- 

 stance, brown or whitish, unicolored or with a peripheral white 

 zone, frequently hairy. Umbilicus open or minute ; form globose- 

 depressed, with convex or conoid spire, and rounded or angular peri- 

 phery. Aperture lunate, the lip acute, expanded below, usually 

 thickened within, the basal margin rarely 1 or 2 toothed. Type 

 H. dnctella (See pi. 55, figs. 20 to 30). 



Jaw arched, thin, with delicate low riblets which denticulate the 

 margins but feebly (pi. 70, figs. 31, 39). Radula as usual in ground- 

 snails. Median cusps long and acute, the side cusps usually devel- 

 oped though small on middle teeth. Ectocones well developed on 

 lateral teeth. Marginals with long simple or bifid inner and smalt 

 simple or split outer cusp. 



Genital system (pi. 70, figs. 30-41) ; penis continued in an epiph- 

 allus which bears the retractor and ends in a short flagellum and 

 the vas deferens. Dart sack single or repeated, with or without 

 accessory sacks, the contained dart or darts cylindrical below with 

 short blades at apex. Mucus glands inserted on vagina above the 

 dart sack, consisting of several independently inserted or grouped 

 tubes. Right eye-retractor passing between branches of genitalia. 

 Dart apparatus sometimes entirely lacking by degeneration. 



Distribution, Europe, North Africa and Western Asia. 



The genus is not very fully represented in the fossil series as now 

 known, although a moderate number of forms are found extending 

 as far down as the Oligocene of middle Europe. I do not know 

 that any Eocene or earlier species can be referred with certainty to- 

 the group, but it is not unlikely. 



The prominent features of this genus are (1) the thin dull-colored 

 shell, in which calcareous matter is never predominent, a hairy 

 coat is often developed, and the lip is not reflexed ; (2) the thin 

 jaw with many slight riblets ; (3) the normal disposition of the right 

 eye-retractor, the short flagellum, frequent doubling of the dart sack 

 and the separation of mucus glands from the latter. These features 

 separate the genus from Helicella, which is allied in form of the 





