ScROBicui,ARiA. MOLLUSCA. Glossus. 363 
rivers of Western Africa, as high as twenty miles from 
the sea. 
Genus Scrobiculaiua. — This genus, forming the 
type of a small family Scrobiculariidai, has an oval, 
thin, compressed shell, and the cartilage is internal, and 
situated in a shallow, triangular pit. The species of 
shell upon which the genus is founded, is a native of 
our own shores, and is found living buried vertically 
five or six inches deep. The most remarkable circum- 
stance in the history of this shell, perhaps, is the num- 
ber of names by which it has been described. 
Family — MACTRID.®. 
The Mactras have an equivalve, trigonal shell, which 
in some is close and in others slightly gaping, and in all, 
covered with a thick epidermis. Tlie hinge is furnished 
with two diverging cardinal teeth in each valve, the 
central one being laminar and folded, and usually with 
an anterior and posterior lateral tooth, those of left 
valve being single, and those of right double. The 
cartilage is internal, and is placed in a deep triangular 
pit behind the cardinal teeth. The pallial sinus is 
short and rounded. 
The true Mactras {Mactrince) have a more or 
less trigonal shell, nearly closed behind. The anterior 
hinge tooth is bifid or triangular, and the lateral teeth 
are distinct, well developed, and laminar. They inhabit 
sandy coasts at various depths, though the majority, and 
especially the larger kinds, are littoral. The animals 
are active and powerful for their size, and live buried 
in the sand at a small depth beneath its surface. “ The 
foot can be stretched out considerably, and moved about 
like a finger; it is also used for leaping.”- — ■( Woodivard.) 
The British species afford food to the star-fishes and 
whelks, and Mr. Alder informs us that one species, 
Mactra suhtruncata, a common one in the island of 
Arran, is collected by the natives to feed their pigs 
with. There are several genera in the Mactrinm, 
characterized chiefly by the position of the ligament. 
These genera are Mactra, ScMzodesma, Spisula, Midi- 
nia, and Onathodon. The family is represented in 
Plate 10, fig. 3, by a British species, Mactra stultorum. 
Genus Gnathodon. — This genus has an oval, ven- 
tricose, thick and smooth shell, with eroded beaks and 
an olive epidermis. The hinge is furnished with two 
cardinal teeth in one valve, and one in the other, and 
the lateral teeth are doubled in the right valve, elon- 
gated and striated transversely. The ligament is 
internal and placed in the upper edge of the deep, cen- 
tral cartilage pit. 
GNATHODON CUNEATUS— perhaps the only species 
of the genus — is a native of New Orleans, and was 
formerly eaten by the Indiana. It lives in vast num- 
bers in the extensive flats below Mobile, burrowing 
three or four inches beneath the surface of the sand, in 
which numerous depressions indicate where they are 
to be found. The water there is only brackish, though 
|there is a tide of three feet. Banks of dead shells, three 
or four feet thick, are found twenty miles inland, and 
Mobile is built on one of these banks. “ A deposit 
composed entirely of two existing shells in a subfossil 
state, the Cyrena Carolinensis, and more especially the 
Rangia cyrenoides of Bes Moulins { = Gnathodon 
cuneatus), extends along the whole shore of the Gulf 
of Mexico from Pensacola to Franklin in Louisiana, 
bends round Mobile bay, Lake Poutchartrain, and 
ranges across the delta of the Mississippi immediately 
above its marshes, a total distance of nearly three hun- 
dred miles, and probably much further ! It is remark- 
able that the shells occur in beds with scarcely any 
admixture of sand or earth, and they are consequently 
found extremely useful in repairing roads and paving 
the streets of the city. They are dug from the surface 
of the soil, both on the main shore and the islands ol 
the bay. These deposits border the bays of the Gulf 
of Mexico, between Mobile and New Orleans, and they 
occur in the vicinity of Franklin, Louisiana. The 
Ohandeleur Isles, between Mobile bay and the delta of 
the Mississippi, consist of depositsof these shells covered 
by a fertile soil.” {Johnston — Report of British Associa- 
tion.) The road from New Orleans to Lake Pontchar- 
train (six miles) is made of Gnathodon shells procured 
from the east end of the lake, where there is a mound 
of them a mile long, fifteen feet high, and twenty to 
sixty yards wide. In some places it is twenty feet above 
the level of the lake. — {Lyell, in Woodioard.) 
The Lutrarias or “Otter shells” {Liitrariinai) 
have oblong or elongate shells, gaping at both ends 
and covei'ed with an epidermis. The plate on which 
the cartilage is fixed is prominent, and has one or two 
small teeth in front of it in each valve. The lateral 
teeth are very small, rudimentary, often obsolete. The 
pallial sinus is deep, horizontal. The Otter shells are 
found in various parts of the world. They live habi- 
tually buried in the mud, fixed in a vertical position, 
and are principally met with in estuaries, at depths 
varying from low water to twenty fathoms. Several 
genera have been found in this group. 
Family— PAPHIIDJU. 
This family, composed of the genera, Pcqdiia, Meso- 
desma,Donacilla, and Anapa, have an equivalve, closed 
shell, with the cartilage in an internal pit, and with a 
simple compressed cardinal tooth and a rudimentary 
process in the place of the second tooth. The form oi 
the shell is various. The Paphias are ovate, somewhat 
trigonal, truncated behind, and slightly keeled. The 
Mesodesmas are transversely ovate shells, with the hinge 
in the middle. The DonacillcB are wedge-shaped shells, 
with the hinge at one end. These shells live in sands 
in New Zealand and other parts of the world, and some- 
times are found in estuaries. 
Genus Glossus (= Isocardia), the “Heart Cockle.” 
— This genus, forming the type of a small family, 
Glossidai, has a peculiar heart-shaped shell, whence its 
English name. It is ventricose, equivalve, smooth or 
furrowed externally, with prominent contorted beaks, 
and a hinge consisting of two very oblique cardinal and 
two lateral teeth in each valve, the anterior being some- 
times obsolete. The ligament is external, and there is 
no pallial sinus. Mr. Bulwer, who had an opportunity 
of watching our British species, Glossus cor, alive, 
tells us that on being placed in a vessel of sea-water, the 
valves of the shell gradually opened; the feelers or 
