GASTROPODS. 
349 
figured on page 344 is found all over Europe, and ranges even as far as Afghanistan, 
The character of the radula is shown in the figure on the next page. 
The family Oncidiidce includes about fifty shell-less air-breathing molluscs, 
somewhat slug-like in general appearance, hut provided with a thick mantle covering 
the whole dorsal region. This is frequently more or less tubercular, some of the 
tubercles being furnished with eyes which, simple as they are in structure, are 
identical in type with those of the Yertebrata. These snails live on the seashore 
or in brackish marshes, eating nothing but sand, but, of course, only digesting the 
nutritious organic particles contained in it. Professor Semper has given an 
account of their habits, and how they are pursued by certain fishes (Perio'ph- 
thalmus), which come ashore after them. One species, 0. celticum, is found in 
Cornwall and South Devon, others occur in America and the Pacific. 
Basommato- The numerous forms belonging to this group, comprising the rest 
phora. 0 f the Pulmonata, differ from those already indicated, in having the 
eyes situated at the base of the 
tentacles, as in the marine whelks 
and periwinkles, instead of at the 
tips. An external shell is always 
present, and capable of containing 
the entire animal. The members 
of th.e family Auriculiclai mostly 
Eariet Shells, inhabit salt or brack- 
Auricuiidse. j s p marshes, and were 
formerly regarded as marine mol¬ 
luscs. The shells generally are 
rather solid, of different forms, but 
usually with narrow apertures, more or less contracted by teeth. The internal 
septa between the whorls of the spire are often absorbed or dissolved, excepting 
that between the last and penulti- 
Pythia scarabaius (nat. size). 
mate volutions. Some species of the 
typical Auricula have large heavy 
shells, and are met with in mud- 
banks and in swamps, in the Indian 
Archipelago. Those belonging to 
Pytliia have oval, compressed shells, 
with toothed apertures, and occur 
in great numbers in most places in 
woods near the sea, are wholly ter¬ 
restrial in their habits, and feed on 
decayed vegetation. One member of 
this family ( Carychium minimum) 
is found in Great Britain, and on the Continent. It is an extremely small 
shell, less than the tenth of an inch in length, transparent, glossy, having 
three teeth-like projections within the aperture. It hides away at the roots 
of grass, among moss, dead leaves, or under stones or dead wood, in damp 
situations. 
earlet shell, Auricula judae (nat. size). 
