85 s1YALINIA RADIATULA. 
Diagnosis.—H. radiatula may be distinguished from //. pura its 
closest ally, by its much more glossy aspect, smaller umbilicus, and the 
very distinct and regular radial striation. From the young of Z. nitidus 
and Z. excavatus it may be distinguished by its size and number of 
whorls and by the character of the striz and umbilicus. 
Original Description.—‘‘ H. radiatula mihi. Shell depressed, horn coloured, 
rather shining, transparent, regularly striated ; with 35 to 4 whorls, flattened at 
their junction with the inner ones, over which the strive appear continuous and 
strongly marked, giving the shell a radiated appearance under a magnifier; the 
outer whorl rather large in proportion to the rest ; underside smooth without any 
whiteness ; umbilicus moderately large ; diameter 1} tenth of an inch. 
Animal black. 
In wet moss, not uncommon. 
This species may be distinguished from the young of the foregoing [H. nitidula] 
to which it bears some resemblance by the regular and more distinct strive, and 
particularly by the flatness of the whorls at their junctions. The same characters 
serve to divide it from the young of the two following species, H. nitidula and 
H. excavata.”—J. ALDER, Trans. N.H. Soe. N.D. & N., vol. i., pt. 1, p. 38, 1830. 
Original Description.—‘‘66. Helix (Hammonis) testa umbilicata planiuscula 
anfractibus qvatuor, apertura subrotundo-lunata. 
In this way I distinguish a small land shell which is found here [Sondmor] 
under stones and rotten wood in fields. |The shell resembles 
in shape the so-ealled ‘Cornua hammonis,’ but is somewhat —~2 | 
flat, and exhibits 4 whorls on the upper side, of which the KS) (23 
first almost equals the rest of the shell. On the under-side by : 
there is only 1 whorl, with a round hole in the middle. The Peers "Gea 
aperture is similar to the preceding [Vitrina] but proportion- — Selsk. Skrift., pl. vi. f. 16. 
ately less and more encroached upon by the penultimate 
whorl. It is of a horn-colour, but usually somewhat yellow near the apertural 
margin. The shell is very fragile and translucent, and the animal within is a 
blue-black snail with 4 horns.”--HANS STROM, Trondj. Selsk. Skrift., 1765, iii., 
p. 435-6, pl. vi., f. 16. 
Description. —ANIMAL with a slender Boby, blunt anteriorly and pointed behind ; 
HEAD and DORSUM bluish-black, with widely-set dorsal grooves, and with flat and 
indistinct tuberculation ; sides and hinder part of body grey, slate-coloured, or 
almost colourless, with coarse isolated tubercles on the TAIL; MANTLE erey ; 
OMMATOPHORES long and somewhat bulbous at end; the BLACK RETRACTORS 
visible through the tissues ; LOWER TENTACLES short, only about ith the length 
of the ommatophores ; FOOT-SOLE with distinet pedal furrows, trifasciate beneath, 
the median area pale grey or whitish, and the,outer zones perceptibly darker. 
SHELL only slightly convex above and below, remarkably glossy, thin and 
somewhat translucent, of a horn colour of variable intensity in different individuals 
Fic. 129.—Outlines of the basal 
and frontal aspects of Hyadlinia 
vadiatula (Alder) from Murlough 
Bay, co. Antrim x 5. 
(After camera lucida drawings by 
Mr. G. H. Clapp). 
Fic. 130.— Surface sculpture of 
the ante-penultimate whorl of 
Hyalinia radiatula var. viridula 
(Menke), from Shipley glen, Yorks., 
Mr. F. Booth, x 70. 
(After micro-photo. by Mr. J. W. 
Jackson), 
Fic. 129. Fie. 130. 
and from. different localities, slightly paler below, regularly and beautifully 
sculptured across the whorls from apex to periphery by strong, curved, and closely- 
set radiating strive, which are continued more faintly to the umbilical region ; very 
fine and delicate spiral striation only perceptible under a lens is also present on 
the upper surface; SPIRE slightly exserted ; SUTURE shallow ; WHORLS about 43, 
convex, the last whorl somewhat laterally dilated ; MOUTH somewhat oval, some- 
times thickened by a slight marginal rib; UMBILICUS narrow but deep, disclosing 
all the internal spire, 
