Gasteropoda. MOLLUSCA. Gasteropoda. 
cclxvii 
Family LIMACINID.®. — One genus und two 
species comprise tliis fiunily. The shell is spiral, 
transparent, witli a distinct spiral and vitreous 
operculum. Heterofuscus balea was found along the 
coast, from Cape Cod northwards, by Stimpson, who 
named it Spirialis gouldi. It is minute, only one- 
tenth of an inch in length, and resembles an ordinary 
shell of Gasteropod. H. retroversus is a species 
found abundantly at Nahant by Mr. Alex. Agassiz. 
An interesting account is given of its habits in 
Gould’s Invertebrata of MassacJiusetU. 
Order— GYMNOSOM A'l’ A . 
The body in this order is naked, having no shell. 
'I’he head is distinct. 'I'here are two or four wings at 
the junction between the head and the body, with a 
central intermediate lobe or rudimentary foot. The 
gills are exterior. 
Famii.y OLIONID.®.— 'I’he animal is fusiform ; 
the head with a series of conical prominences on 
each side. There are two wings, with a central, foot- 
like appendage between them. 'I'here are two genera. 
Class— GASTEROPODA. 
'I'liis great division in the Mollusca is character- 
ized by individuals having a distinct head, which is 
furnished with eyes and tentacular appendages or 
feelers. 'The body is usually protected by a spiral or 
conical shell. 'The lower part of the body is formed 
into a thickened, expanded creeping disc or foot. 
'J’he Gasteropods, including the Land Snails, Sea 
Snails, Whelks, etc., are regarded as particularly 
typical of the Mollusca, presenting all the leading 
features of the class organization in a prominent de- 
gree. 'J’hey are less like the Fishes than the Cephal- 
opods, and less in resemblance to the Articulates 
and Zoophytes than the Bivalves. 'I’he ordinary and 
characteristic mode of locomotion is exemplified by 
the common garden Snail, which creeps by successive 
expansion and contraction of its broad foot. Gas- 
teropods are nearly all unsyminetrical. 'I'he body is 
coiled spirally, and the respiratory organs of the left 
side are usually undeveloped, more or less. In the 
Ghil.on and Dentalium the branchimand reproductive 
organs are repeated on each side. A few species are 
viviparous, including the Helices; the rest are egg- 
bearing. Gasteropods have what is termed an odon- 
toplm-e — a “ tooth-bearer,” or lingual ribbon, situated 
within the mouth, which is beset with fine chitinous 
teeth. 'I'he odontophore is a curiously-developed 
organ, which has been described by Huxley as con- 
sisting “ essentially of a cartilaginous cushion, sup- 
porting, as on a pulley, an elastic strap, which bears 
a long series of transversely-disposed teeth The 
ends of the strap are connected with muscles, at- 
tached to the upper and lower surface of the hinder 
extremities of the cartilaginous cushions. 'J'hese 
muscles, by their alternate conti’actious, cause the 
toothed strap to woik backwai'd and forward over 
the end of the pulley formed by its anterior end. 'I’he 
strap consequently acts after the fashion of a chain- 
saw upon any substance upon which it is applied.” 
'I’his lingual ribbon, as well as the hard, horny sub- 
stance which closes the aperture to the Gasteropods, 
is important in the matter of classification, both be- 
ing much used at present as guides. 'I'he teeth of 
the former are particularly regarded. 'I’he Gastero- 
pods form two natural groups, one comprising the 
air-breathing forms, and the other those breathing 
through the medium of water, like the Fishes. 'I’hose 
of the first group are apparently perfect when born. 
differing only in size from the parent. 'I’he water 
breathers have a small nautilus-like shell at first, 
which conceals them entirely at will, and which is 
closed by an operculum. 'I’hey do not creep, but 
swim with ciliated fins, which are formed upon the 
sides of their head. By this means Nature has pro- 
vided that though they are quite circumscribed when 
fully grown, they may be widely dispersed when 
young. This form of young Mollusk may be fairly 
compared to the larva of insects. 'I’he young of the 
fresh-water Gasteropods are perfect, though they 
may not be seen by the naked eye. Dr. Gill says : 
“'I’he principal modifications of structure are ex- 
hibited in the following groups, to which have been 
assigned the rank of sub-classes: 1. The Diocea ; 
2. The Fulmonifera ; 3. The Opisthobranchiata ; 
4. The Polyplacophora ; 5. The Frosopoceplmla ; 
6. The Fteropoda.” Under the class Gasteropoda, 
Binney gives the following arrangement of shells 
found on the coast of New England : 
Famii.y BULLID/E embraces seven genera and 
fifteen species. Many of them are delicate, bubble- 
like shells, as the family name imports (see Plate 
4, figs. I, 2, 3, and 4). .Several species are found in 
the stomachs of God and other Fishes taken in the 
deep water on Grand and George’s Banks. We have 
frequently taken them in this manner from Fishes 
caught of! Nahant. 
In the order Nudibranchiata there are six families 
of very interesting forms. 'I’he creatures which are 
included here are naked, having no shells, but many 
are beautifully decorated with branching breathing 
organs and tentacular-like appendages (see Plates 
4, 5, 6). Many species are found clinging to masts 
and spars around the dock-yards. Several forms 
have been dredged by Dr. Stimpson in the waters 
around Boston Harbor, and at Grand Menan. 'I’he 
beautiful Dendronotus arborescens is found in pools 
among the Algae at low tide along the shores of Na- 
haiit and Swampscott. Eleven species of Eolis are 
now known. 'I’he extreme beauty of some, and outre 
appearance of nearly all, render them objects of great 
interest. Many are like Caterpillars in their aspect 
and mode of locomotion. 
Family GH1TONBIDA3 contains the peculiar 
multivalve shells, shield-shaped, and composed of 
numerous pieces. A few small species are found on 
