26 
T H E 'I'ASM A NIA N N AT U R A LIST. 
CLASS II. —Gastropoda (Belly-footed) comprises those Mollusca 
which, like the common snail, creep on the under surface of the body, 
and, with one exception (Chiton, Fig. 16), their shells are univalve (i.e., 
composed of one piece). The aperture, whence the animal issues, is 
called the mouth : and its outer edge the lip ; each turn of the shell is a 
whorl; the last and largest the body whorl, the whorl from the top at the 
apex down to the mouth form the spire : and the line where the whorls 
join each other is called the suture. The axis of the shell around which 
the whorls are coiled is sometimes open or hollow, and the shell is then 
said to be umbilicated (as in Fig. S); when closely coiled a pillar of shell 
or columella is left (as in Fig. 2). Sometimes the corner of the mouth 
farthest from the spire and next the columella is produced into a channel, 
the anterior canal (see Fig. 2). Most Gastropods are dextral— that is to 
say, the mouth is to the right of the axis as you look at it ; a few, how¬ 
ever, are sinistral (like Physa, Fig. 20), whilst reversed varieties of both 
kinds are met with occasionally. 
Gastropods of the first order have comb-like gills placed in ad¬ 
vance of the heart, and hence are termed Prosobranchiata. They are 
divided into two groups, (a) Siphonostomata (Tube-mouthed), in which 
the animal has a long proboscis and a tube or siphon from the breath¬ 
ing chamber that passes along the anterior canal of the shell, which in 
this group is well developed (as in Fig. 2). They have a horny 
operculum or lid with which to close the aperture, (b) Holoslomata (or 
whole-mouthed). In these the siphon is not produced, and does not 
want to be protected, accordingly the mouth of the shell is entire, i.e., 
has no canal (see Fig 9). The operculum is horny or shelly. 
The former (Group a) includes several families : — 
1. The Strombida , comprising many large showy species, some of 
which are used for cameo cutting. None are found in Tasmania. 
2. The A/uric idee, containing Mu rex, of which we have several 
species more or less spiny, and Fusus, or long-tailed whelks, with 
several fine Tasmanian species (Fig. 2). 
3. The Buccinidiz, including Nassa, Cominella , Purpura (Fig. 
3), and Oliva, all with representatives here. 
,4. The Cassididic, or ‘Helmet shells/with Cassis (Fig. 7) and 
Lotorium, with several fine species; the large L. spengleri is a common 
form (Fig. 4). 
5. The Conidic, whose type, the * Cone shell ’ (Fig. 1), is so 
abundant in tropical seas, but only represented here by one fair sized 
and one minute species. And also the Fleurolomidc e, an immense 
genus of small but beautiful shells, well represented here, but usually 
found in deep water. 
6. The Volutidcc, embracing the Valuta, Mi fra, and Marginella . 
They have solid shells, usually polished or enamelled, and with several 
strong plaits or folds on the columella (see Fig. 5). We have several 
very "fine volutes, including one of the largest (i.e., l\ mamilla). 
