Involute.] 



MOLLUSCA. 



53 



36. Helix radiatula, pi. XVIII,* f. 5, 6. 



Helix radiatula, Alder, Cat., p. 12, No. 50; lb., Mag. Zool. 

 and Bot., II, p. 107; Jeffreys, Linn. Tr., XIII, p. 511; Thomp- 

 son, Ann. and Mag. Nat. Hist., VI, p. 33 ; Helix striatula, 

 Gray, Med. Rep., 1821, p. 239; Helix brevipes, Turton, Man., 

 p. 65, pi. 5, f. 50. 



Shell pellucid, diaphanous, horn-coloured, depressed ; spire 

 but little elevated above the body volution, and consisting of 

 three volutions, which are particularly flat at their junction ; 

 body large, in proportion to the spire ; upper parts covered 

 with regular, continuous, longitudinal stria;, and producing a 

 radiated appearance ; base smooth, with a moderately sized 

 umbilicus. This is an exceedingly minute species, its diameter 

 hardly exceeding the twentieth of an inch. 



Its habitat is in wet mossy ditches, and in damp wooded 

 localities. 



Distinguished from the young of H. zonites, by the great 

 flatness of the volutions at their lower side, and by the striae 

 being more regular and decided. 



This shell occurs in many parts of Britain. Mr. Thompson 

 gives as localities, Dovedale, Derbyshire ; the Falls of Clyde, 

 Lanarkshire ; and Ballantrae, Ayrshire ; and in Ireland, he says 

 it is widely distributed, namely, Londonderry, near Dublin, 

 Downshire, Antrim, Tyrone, Cork, and Queen's County. 



37. Helix crystallina, pi. XVIII,* f. 7, 8. 



Helix crystallina, Muller, Verm., II, p. 23, No. 223; Pfeiffer, 



I, p. 46, pi. 2, f. 36; Drapemaud, p. 118, pi. 8, f. 13 to 28; 

 Gray, Med. Rep., 1821, p. 239 ; Alder, Mag. Zool. and Bot., 



II, p. 108; Turton, Man., p. 58, f. 42; Jeffreys, Linn. Tr., 

 XIII, p. 341 and 511 ; Thompson, Ann. and Mag. Nat. Hist., 

 VI, p. 34; Rossmassler, VIII, p. 37, pi. 39, f. 531, var. ; 

 Helix vitrea, Brown, Edin. Journ. Nat. and Geo. Science, I, 

 p. 12, pi. 1, f. 12, 13, 14; Zonites crystallinus, Leach, Moll., 

 p. 105. 



Shell thin, depressed, of a very glossy, crystalline, greenish- 

 white colour ; spire with five well defined, gradually decreasing 

 volutions, terminating in an extremely small, hardly-raised 

 apex ; base of the shell a little convex, provided with a small, 

 but deep umbilicus ; aperture semi-lunate, and enveloping the 

 body. Diameter three-sixteenths of an inch. 



This species may at once be distinguished from its con- 

 geners, by its extremely glass-like aspect, the number of its 

 volutions, and in the body one being but little thicker than the 

 lower volution of the spire. 



The H. crystallma is not uncommon in many parts of Eng- 

 land. It was first found in Scotland by my esteemed friend 

 James Gerard, Esq., who detected it in an old wall at Corstor- 

 phine Hill, near Edinburgh ; where I afterwards found it. 

 Thompson says it is generally distributed in Ireland, occurring 

 in moss, under stones, and upon decaying wood, both in wet 

 and dry situations. He adds, " Some adult specimens which I 

 have collected have had but three and a half volutions, instead 

 of four and a half or five, the ordinary number." I have great 

 doubts of these last mentioned being really the H. crystallina, 

 as one of its strongest characters is, the number of its volutions, 

 in which it is only equalled by the following species. 



38. Helix excavata, pi. XVIII,* f. 9, 10. 



Helix excavata, Bean; Alder, Cat., p. 13, No. 53; lb., Mag. 

 Zool. and Bot., II, p. 107; Thompson, Ann. and Mag. Nat. 



Hist., VI, p. 34 ; Helix lucida, var-, Turton, Man., p. 57, pi. 

 4, f. 39 ; Helix nitida, Jeffreys, Linn. Tr., XIII, p. 339 and 

 511. 



Shell subglobose, transparent, diaphanous, shining, yellowish 

 horn-coloured, and covered with longitudinal, irregular wrin- 

 kles ; body very large ; spire subdepressed, small, consisting of 

 four or five well rounded, close-set volutions, terminating in an 

 obtuse apex ; base considerably inflated, and provided with a 

 large and deep umbilicus, in which may be seen the inside of 

 the volutions, nearly to the apicial one; aperture slightly lunate, 

 or nearly round. Diameter about a quarter of an inch. 



Discovered near Scarborough by Mr. Bean, and has been 

 found by Mr. Alder in Northumberland ; and Thompson says 

 he has seen but one Irish specimen, which was procured at 

 Dunscombe Wood, near Cork, by Miss King, of Cork. 



Its favourite habitat is timber which has been cut down, and 

 under decayed wood. 



39. Helix pura, pi. XVIII,* f. 11, 12. 



Helix pura, Alder, Cat., No. 46 ; lb., Mag. Zool. and Bot., 

 II, p. 108; Thompson, Ann. and Mag. Nat. Hist., VI, p. 32; 

 Turton, Man., p. 59, the description only ; Helix nitidula, var. 

 ft, Jeffreys, Linn. Tr., XIII, p. 511. 



Variety 1. Shell pale horn-coloured. Alder, Mag. Zool. 

 and Bot., II, p. 108. 



Shell nearly white, depressed, somewhat pellucid, and glossy, 

 a little striated, or wrinkled; body large; spire small, with three 

 volutions, placed somewhat oblique; base considerably flattened, 

 provided with a large and deep umbilicus ; base never opaque. 

 Diameter between a fifth and sixth of an inch. 



This shell differsfrom H. crystallina in being larger, more 

 convex, and less glossy ; the volutions are not so closely set, 

 the body somewhat larger in proportion to the spire, with a 

 larger umbilicus, and especially in the fine, regular stria?, of 

 which the H. crystallina is destitute. 



Found near Newcastle-upon-Tyne by Joshua Alder, Esq., 

 and as far as is known, rather a local species in England ; in 

 Ireland, according to Thompson, it is rather widely spread ; 

 its usual habitat being among moss, in sheltered situations. I 

 found it near Cabinteely, County of Dublin. The yellowish 

 horn-coloured variety is most commonly met with. 



Sub-Genus 8 Trigonostoma. — Ferussac. 



Shell subdiscoidal ; apex depressed ; base umbilicated; aper- 

 ture trigonal; outer lip denticulated ; epidermis for the most 

 part hispid. 



40. Helix obvoluta, pi. XVIII,* f. 13, 14. 



Helix obvoluta, Muller, Verm., II, p. 24 ; Helix holosericea, 

 Drapemaud, p. 112, pi. 7, f. 27 and 29 ; Brard, p. 62, pi. 2, f. 

 16, 17; Pfeiffer, I, p. 41, pi. 2, f. 28 ; Rossmassler, I, p. 70, 

 pi. 1, f. 21 ; Ferussac, Prod., p. 38, No. 107; Lindsay, Linn. 

 Trans., XVI, p. 765. 



Shell reddish-brown, planorbiform, depressed both above and 

 below, and largely umbilicated; spire concave, and consisting of 

 five narrow volutions ; aperture triangular ; the outer lip re- 

 flexed, pale red, and provided internally with a small, blunted 

 tooth. Diameter five-eighths of an inch. 



