CHARACTERISTIC DEEP-SEA TYPES. — BRACHIOPODS. 15 
* Challenger " from the deepest water in which any bivalve has 
yet been found living. 
There are almost innumerable illustra- 
tions of. beauty, adaptation, or unusual 
characteristics which might be cited, but 
to those unaequainted with the objects 
themselves such an enumeration would 
be tedious. The enthusiastic student and 
collector alone can find pleasure in what 
Fig. 312. — Vesicomya 
would seem to most people a dry com- vetusto. Hh 
bination of a lexicon and a catalogue. 
BRACHIOPODS. 
Until quite lately brachiopods were rarities in collections ; but 
since the days of dredging expeditions we know that they are 
very numerous at favorable localities on rocky or stony bottoms. 
They do not seem to penetrate very great depths, naturally 
finding no point of attachment in the soft ooze of the deep 
waters, and but few species are thus far known to extend beyond 
600 fathoms. The largest known species have been dredged 
from the abyssal region, and young specimens are frequently 
found attached to the older ones. None of the deep-water spe- 
cies have the brilliant coloring characteristic of the common lit- 
toral species belonging to the genus Lingula. The principal 
differences upon which their classification is based are those of 
the so-called loop, the calcified support of the brachia, and the 
struetural details of the valves. 
The recent brachiopods are specially interesting as represen- 
tatives of a group which attained an extraordinary development 
in very early ages, and has been represented in all formations. 
They have a most extensive geographical distribution, and a 
great bathymetrical range. They are found at all levels, from 
pools left by the tides to-a depth of 3,000 fathoms. The num- 
ber of living species is small compared to the hosts which flour- 
ished in the silurian, devonian, and carboniferous, from which 
time they have steadily diminished in number. Nearly 1,700 
species occur in the silurian, but there are not more than 120 
known from the seas of the present day. Their position in the 
