202 
T. Davidson — What is a Brachiopod ? 
bution of the recent species, as well as to tbe marine depths they 
inhabit or prefer. 1 
This important knowledge is mainly due to the numerous well- 
conducted and equipped dredging expeditions carried on by private 
individuals, and by the Governments of the leading maritime States. 
Previous to these investigations the data we possessed with respect 
to the habitat, and ranges of depth were, in most cases, vague and 
unsatisfactory. It has also been ascertained that the Brachiopoda are 
mucli localised, and usually occur in great numbers in their favourite 
haunts. 
We can know nothing with certainty in respect to the i'anges of 
depth at wliich the extinct species lived; but some idea as to their 
probable depths can be surmised froin a study of recent forms. 
As far as our present information will carry us, the Tretenterata 
( Lingula , etc.) do not appear to have been found at a greater depth 
than froin 13G6 to 2000 fathoms. 
Lingula abounds in particular haunts. and lives at about half tide- 
mark, and partly buried in mud ; or at depths varying from three or 
four inches from the surface of the sea to seventeen fathoms. Prof. 
Morse describes a species wliich he found in vast numbers in a sand- 
shoal at low- water : the peduncle, six times the length of the shell, 
was partly encased in a sand tube (Pl. X. Fig. 5). He observed 
likewise that this species (Lingula pyramidata) liad the power of 
moving over the sand by the sliding motion of the two valves, using 
at the same time the fringes of setai, wliich swing promptly back and 
fortli like a galley of oars, leaving a peculiar tract in the sand. In 
the motion of the setse he noticed the impulse commencing from 
behind, and running forward. 
Discina has been found attached to stones at low- water mark, and 
has been dredged from depths ranging from five to nearly 2000 
fathoms; very often clustered together in vast numbers, and adher- 
ing, in all stages of growth, by their peduncle to the surface of 
the shell of their neighbour, one above the other, tili they formed a 
living mass of considerable breadth and thickness. 
Crania is found in great numbers adhering to stones and sliells at 
depths of from eighteen to 530 fathoms. Lucas Barrett informs us 
that the cirri are protruded, but not the brachial appendages, beyond 
the margin of the shell, and that the valve opens by moving upon 
the straight side of the hinge without sliding the valve. 
The genera and species of Clistenterata lived at depths ranging 
from about half tide-mark to 2600 fathoms. At that great depth, 
between Kerguelen Island and Melbourne, the “ Challenger ” Ex- 
pedition brought up, among other things, “a very elegant little 
Brachiopod another species was dredged by the same expedition 
three hundred miles east of St. Paul’s Bocks, Atlantic, at a depth of 
1850 fathoms, but the larger number of species live at depths of 
from five to three, or four hundred fathoms, usually attached by their 
1 The reader is referred to an important paper upon this subject by Prof. Edward 
Suess, über die Wohnsitze der Ihacbiopoden (Aus dem xxxvii. und xxxix. Bande, 
Wien, 1859, 1860, Akademie der Wissenschaf len besonders abgedruckt). 
