LAMP-SHELLS. 
43i 
Hingeless Group. 
UPPER VALVE AND ANIMAL OK 
Crania (magnified). 
very remarkable by the long, spirally-coiled and calcified arms. Spirifer was 
very abundant in the Palaeozoic epoch, but died out with the Lias. 
The second order of the Brachiopods (Ecardines), or those whose 
shells are without hinges, consists of but four families, two of which 
may be briefly described. The unstalked genus Crania is widely distributed, 
both geologically and at the present time. Its structure is so peculiar that it 
forms a family by itself ( Craniidce ). The shell is attached to some submarine 
object by the ventral valve; the dorsal valve is lid¬ 
like, and the two valves connected, not by a hinge 
or interlocking processes, but simply by muscles. The 
best-known of the four living species (here figured) of 
the northern seas, is almost always found in company 
with Terebratulina, which, however, it does not follow 
into the seas of Northern America. . 
The last family to be described, the Lingulidce, 
is also one of the most interesting. It existed in 
the oldest fossiliferous strata, and is still found living 
chiefly near the shores of the warmer seas. It may be regarded as perhaps the 
very oldest of the Brachiopods. Indeed, if we may look upon the hinge which 
characterises the other order as a specialisation, the hingeless forms are clearly 
the older and more primitive. The shell of a Lingula is thin and horny, almost 
flexible, and green in colour. The valves are almost exactly similar, and, as we 
have seen, they are not hinged together; and, further, they have no processes for 
the support of the thick, fleshy spiral arms. No 
living Lingula is now found in European seas, but 
L. pyramidata occurs on the American coasts, and 
another, L. anatina , in the Philippines. The stalk 
of the former, which is nine times as long as the 
body, does not become attached, but moves like a 
worm, and again, like certain worms, makes tubes 
out of sand into which it can withdraw. The 
Lingulidce generally live in holes in mud, the 
bottom of which is lined with sand. The shell- 
covered body projects above the mud to open and 
feed; on being alarmed, it shuts and disappears 
below the surface. The cilia at the mantle-edge 
form a fine sieve which prevents foreign particles 
from entering the gills. The length of life of L. 
pyramidata is not more than a year. The sim¬ 
plicity of the shell of Lingula , which may best be 
compared with the cartilaginous structures at the 
anterior end of a chaetopodous annelid, and its occurrence in the oldest strata in 
which Brachiopods are found, seems to justify the conclusion that it stands nearest 
of all the class to the worm-like ancestor. 
Lingula pyramidata (nat. size). 
H. and M. BERNARD. 
