MOLLUSCA. 
53 
Involute.] 
36. Helix radiatdla, pi. XVIII,* f. 5, 6. 
Helix radiatula, Alder, Cat., p. 12, No. 50; Ib., Mag. Zool. 
and Bot., II, p. 107; Jeffreys, Linn. Tr., XIII, p. 511; Thomp- 
son, Ann. and Mag. Nat. Hist., VI, p. 33 ; Helix striatulU) 
Gray, Med. Rep., 1821, p. 239; Helix hrevipes, 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 strise, 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 dustributed, namely, Londonderry, near Dublin, 
Downshire, Antrim, Tyrone, Cork, and Queen’s County. 
37. Helix crystallina, pi. XVIII,* f. 7? 8. 
Helix crystallina, Muller, Verm., H, p. 23, No. 223; Pfeiffer, 
I, p. 46, pi. 2, f. 36; Drapernaud, p. 118, pi. 8, f. 13 to 28; 
Gray, Med. Rep., 1821, p. 239; Alder, Mag. Zool. and Bot., 
H, 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, VIH, 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 tbree-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 tbe body one being but little thicker than the 
lower volution of the spire. 
The H. crystallina 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; Ib., 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., XHI, 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; Ib., Mag. Zool. and Bot., 
H, p. 108; Thompson, Ann. and Mag. Nat. Hist., VI, p. 32; 
Turton, Man., p. 59, the description only; Helix nitidula, var. 
13, Jeffreys, Linn. Tr., XIII, p. 511. 
Variety 1. Shell pale horn-coloured. Alder, Mag. Zool. 
and Bot., H, 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 differs from 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 striae, 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. — Fh'ussac. 
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, 
Drapernaud, 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. 
o 
