BltAUlIIOi'ODA. MOLLUSCA. Tekeueatuliu^e. 37y 
Another peculiarity in the structure of the Brachio- 
range both of climate and depth, as well as time, than 
podous Mollusca is their respiratory system. True 
any other Mollusca known. They are found in tropical, 
gills are altogether wanting, and accordingly, by some 
temperate, and arctic seas ; in shallow pools left by 
of the earlier conchologists, these oral or fringed arms 
the retiring tide, and at the greatest depths explored 
were considered as subsidiary to respiration and the 
by the dredges ; whilst, in time, they are found fossil 
aeration of the blood ; but Professor Owen, in his 
in the miocene tertiary, and in the oldest Devonian 
masterly paper in the Zoological Journal, from which 
strata. Indeed the oldest form of organic life at pre- 
we have already given an extract or two, shows that 
sent known, both in the Old and New world, is a 
these processes are carried on by the mantle. The 
Lingula. At present there are only between seventy 
true branchial vessels, he says, are ramified in rich 
and eighty recent species known, whilst of extinct 
profusion upon the inner surface of the lobes of this 
forms upwards of one thousand have been described. 
part of the body, and consequently it forms the chief, 
The class Brachiopoda is divided into two sub- 
if not the sole respiratory organ. “ In this profuse 
classes — I. An(;ylopoda, and II. Helictopoda. In 
distribution of vessels over a plain membraneous ex- 
the Ancylopoda, the oral arms are recurved ; not 
nansion,” says the Professor, “ we perceive the simplest 
extensile, or only at the tip ; and are affixed to shelly 
construction of the water-breathing organ, oxbranchia." 
appendages on the disc of the dorsal valve. The 
In some of the Brachiopods the ova are developed in 
mantle is adherent to the shell, the substance of which 
these large branchial veins, and in others they are 
is pierced by numerous minute perforations. In the 
developed in vascular sinuses on each side of the body. 
Helictopoda the oral arms are elongate and regularly 
Nothing accurate is known respecting the development 
spirally twisted when in repose. The mantle lobes 
of the young, but they are believed to be, in their first 
are merely applied to the inner surface of the shell, the 
stage, free and able to swim about until they meet with 
surface of which is not punctured. 
a suitable position. Some of them appear to attain 
The sub-class Ancylopoda is divided again into two 
their full growth in a single season, and all, probably, 
orders — I. Ancylobkachia, and II. Cryptobraciiia. 
live many years after they have become adult. The 
The Aneylohrachia have the oral arms affixed to 
species are all marine, and are found attached to 
calcareous lamellae, forming a loop attached to the 
branches of coral, hanging from the under side of 
hinge margin of the dorsal valve, and more or less pro- 
shelving rocks, or abiding in the cavities of other shells. 
miuent in its cavity. The animal is generally attached 
They are seldom found on clay beds ; but where the 
to marine bodies by a tendinous peduncle. The Cryp- 
bottom consists of calcareous mud they appear to be 
tohrachia have the oral arms sunk into grooves in the 
very abundant, mooring themselves to every hard sub- 
convex centre of the inner surface of the ventral valve. 
stance on the sea bed, and clustering one upon the 
The shells are generally attached by the outer surface 
other.— ( Woodward.) The Brachiopods enjoy agreater 
of the larger valve. 
Sub-class I. — ANCYLOPODA. 
Order I. — ANCYLOBEACHIA. 
This order contains only two families : — 
teeth of the ventral valve, and a prominent cardinal 
process between them. It is also furnished with a 
hinge plate provided with four cavities, and a central 
ridge or septum. The internal skeleton (see fig. 204) is 
Family — TEREBRATULID^ {The Lamp-shells). 
The shells in this family (see Plate 11, fig. 26, 
attached to this valve, and consists of a slender shelly 
Terebralula australis) are inequivalve, and usually 
loop attached in some genera at its origin to the hinge 
oral or subcircular. They are somewhat like a 
plate, and furnished with oral processes ; in others to 
Grecian lamp in form, and have therefore received 
the septum in the middle of the dorsal valve. The 
the general appellation of Lamp-shells. The valves 
animal is always attached by a peduncle, which passes 
are minutely punctate, sometimes smooth, some- 
through the hole or deep sinus in the apex of the beak; 
times striated. The ventral valve is the larger, 
and the strongly cirrhated, looped, or contorted oral 
and its beak is produced and truncated at the apex. 
arms (described above) are united throughout by mem- 
which is perforated. The foramen or hole is some- 
brane, are folded upon themselves, and are only spiral 
times perfect, at other times it is a deep sinus, uncon- 
at their extremities. The valves are opened and closed 
nected at its lower margin. It is usually separated 
by adductor and retractor muscles, and the peduncle 
from the hinge line by a triangular plate, called the 
is provided with two additional ones. The species. 
deltidium, which is composed of two pieces. The two 
though not numerous, have been distributed through- 
teeth are placed in this valve, situated one on each side 
out a number of genera, whose characters have been 
of the deltidium. The dorsal, and smaller valve, has 
taken chiefly from the structure of the internal skele- 
a depressed beak, two sockets for the reception of the 
ton. They may all be arranged in two tribes. 
