MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 53 
Helicodonta obvoluta (Miiller). 
1767 La Veloutée a bouche triangulare Geoffroy, Coquilles de Paris, p. 46, no. 12. 
1774 Helix obvoluta Miiller, Verm. Hist., pt. 2, p. 27, no. 229. 
1788 — holosericea Gmelin, Syst. Nat., i., p. 3641, no. 186. 
1792 — _ trigonophora Lamarck, Journ. Hist. Nat., li., pl. 42; f. 2; p. 349. 
1792 — bilabiata Olivi, Zool. Adriatic, p. 177. 
1801 Planorbis obvolutus Poiret, Coq. de l’ Aisne, p. 89. 
1819 Helicodonta obvolutwm Férussac, Tabl. Syst., p. 38, pl. 51, f. 4, no. 107. 
1833 Vrigonostoma obvoluta Fitzinger, Syst. Verz. Oesterr., p. 98. 
1837 Vortex obvoluta Beck, Ind. Moll., p. 29. 
1837 Gonostoma obvoluta Held, Isis, p. 915. 
1842 Polygyra obvoluta Gray, Fig. Moll. Anim., pl. 290, f. 13. 
1844 Huphemia obvoluta Menke, Zeitschr. f. Malak., v., p. 74. 
1858 Anchistoma obvolutum Adams, Genera Recent Moll., p. 207. 
ISTORY.— Helicodonta obvoluta (ob- 
voluta, rolled up), belongs to the sub- 
genus FHfelicodonta of Férussac, which is 
wholly or partially equivalent to Chilodon 
and Helicodon Ehrenb., Drepanostoma Porro, 
Contorta Muhlf., Caracollina Beck, and other 
groups cited in the synonymy. 
With this interesting species I feel great 
pleasure in associating my esteemed and 
valued friend, Prof. A. E. Boycott, F.R.S., 
who has given special attention to this species 
and authoritatively elucidated many doubt- 
ful and important points of its structure, and 
to whom many of the special illustrations and 
much of their descriptive matter is due. 
Helicodontu, which Dr. Scharff regards as 
originating in the Lusitanian region, is a 
croup of Mediterranean species in ‘which the 
shell is characterized by an angulate or 
rhombic aperture and a depressed spire, and 
an animal allied in organization to Helicigona 
and apparently linking together that group 
and Hygromia ; its relationship with the 
higher groups is shown by the position of 
the right tentacular retractor which passes 
between the ¢ and @ organs, as in the true or typical Helices, and its 
affinity with Helicigonw is evidenced by the paired mucus glands and 
lanceolate love-dart, which, although wholly or partially lost by degenera- 
tion in the present species, are still possessed by some of the less 
dominant Helicodonts, which are now chiefly restricted to the lofty moun- 
tain ranges of Central Europe. 
This very remarkable phenomenon of the total atrophy of the dart and 
the partial loss of its accessories by the present species though still 
retained by //. holoserica, its less dominant and probably more ancient 
congener, lead us to place less implicit faith im the presence of any par- 
ticular organ or in any specific detail of the internal bodily structure— 
save of the sensory or nervous system—as irrefragable evidence of 
