™, 
196 MONOGRAPH OF BRITISH LAND AND FRESHWATER MOLLUSCA. 
SuB-GENuS Discus Fitzinger. 
Pyramidula ruderata (Studer). 
Helix ruderata Studer, Kurz. Verz., 1820, p. 86. 
— vrotundata B Nilsson, Moll. Suec., 1822, p. 31. 
— umbilicus Marklin, ex. L. Pfeiffer, Symb., 1842, vol. i1., p. 106. 
= Ae Morelet, Journ. de Conch, 1858, vol. vii. 5 Dt. 
— pauper Gould, Proe. Boston Soe. N. H., 1859, vol. Vi., p. 423. 
— cronkhiter Newcomb, Proe. Cal. Acad. Sci., 1865, vol. 1ii., p. 180. 
Discus vruderatus Fitz., Syst. Verz., 1833, p. 9. 
Patula ruderata Held, Isis, 1837, p. 916. 
Euryomphala ruderata eae Ind. Moll., 1837, p. 9. 
Patularia vuderata Clessin, Natur. Ver . Regensburg, 1908, p. 11. 
Pyramidula ruderata Pilsbry, Mannal of Conchology, 1893, pt. 33, p. 46. 
SHELL depressed, but more convex above than below, with a slightly risen 
SPIRE and blunt apex; WHORLS four to five, rounded at the periphery ; of a 
uniform brownish or yellowish-horn colour, and finely but distinctly ridged trans- 
versely. APERTURE Slightly oblique and roundly lunate with an ene peristome. 
UMBILICUS widely and perspectively open. Diam. 5-6 mill. ; alt. 23-3 mill. 
Fic. 250.—Pyramidula ruderata (Studer) X 3, showing basal, frontal, and upper aspects (Finland). 
Diagnosis.—P. ruderata differs from its close ally P. rotundata by its 
more produced spire, fewer and more rounded whorls, and the absence of 
the red-brown freckles so conspicuous in that species, although according 
to Dr. W. H. Dall, the Helix Jocculus of Morelet, a form of P. ruderata, 
is characterized by red-brown or deep-red radiating maculations upon the 
mantle, showing through the translucent shell; but according to Mr. Binney 
this appearance is partially due to fugitive colouring of the shell substance, 
a feature of interest as showing its relationship with P. rotundata, 
Variation.—A white variety, w/bina, is recorded by Miss Esmark as 
found in Norway at Tin in 'elemarken, Roevenzs in Porsangerfiord, and 
Elvenzes in South Varanger (Journ. of Conch., 1886, p. 104); the var. 
albida is cited from Christiania by Dr. Westerlund, and Mantsili, Koli, and 
Pielisjirir in South Finland by Luther, while the “clear hyaline variety ” 
is, according to Rey. 8. Spencer Pearce, frequent in the Upper Engadine, 
Switzerland. The var. viridis is recorded by Dr. Oscar Boettger as found 
rarely with the type at Kusary in governinent of Baku, Transcaucasia ; 
and the var. viridula is noted by Prof. Cockerell from Custer co., Colorado. 
The var. angulosa Mousson is recorded for Tomsk, Irkutsch, Kanitschatke 
and the valley of the Amur; the var. opulens of Westerlund from Kamt- 
schatka, and a var. gorktschana has been described by Prof. Mousson from 
Erivan, ‘l'ranscaucasia. 
Geographical Distribution.— This circumpolar species, which would 
seem to be a weaker forerunner of P. vrotundata, is very widely dispersed 
over the northern regions of the Holarctic realm, extending to the 
furthest limits northwards, and ascending the mountain slopes to as great 
a height as molluscan life can exist, yet “the species is only known in 1 this 
country by its fossil remains, though it is by no menas unlikely that isolated 
colonies may still linger within the limits of the British Isles. 
