BRACHIOPODA. 389 
Crania ; and three pair of adjustor muscles for keeping the 
valyes opposed to each other. Some of these are probably 
inserted in the pedicle. The oral cirri are extremely tender and 
flexible, contrasting with th: stiff and brittle setee of the mantle, 
. \ | y 
RN 
Yh 
WN WAST 
b. S Te a 
Sey 
SY < Ne 
Fig. 197. Dorsal. Fig. 198. Ventral lobe. 
Discina lamellosa, Brod. #- 
u,umbo; f, foramen; d, disk; a, anterior adductors; a’, posterior adductors ; 
c, c', central and posterior adjustors ; 7, external adjustors. The mantle-fringe is not 
represented in Fig. 198, 
which are themselves setose like the bristles of certain annelides 
(e.g. the sea-mouse, Aphrodite). The relation of the animal to 
the perforate and imperforate valves is shown to be the same as 
in Terebratula, by the labial fringe; but the only process which 
can possibly have afforded support to the oral arms is developed 
from the centre of the ventral valve, as in Crania. Baron 
Ryckholt has represented a Devonian fossil from Belgium, with 
a fringed border; but if this shell is the Crania obsoleta of 
Goldfuss, the fringe must belong to the shell, and not to the 
mantle. 
Distribution, 10 species. West Africa, Malacca, Peru, and 
Panama. 
Fossil, 64 species. Silurian—. Europe, United States, 
Falkland Islands. 
In some species the valves are equally convex, and the 
foramen occupies the end of a narrow groove. 
Sub-genus. Trematis, Sharpe. (=Orbicella, D’Orbigny.) 
T. terminalis, Emmons. Valves conyex, superficially punctate; 
dorsal valve with a thickened hinge-margin (and three diverg- 
ing plates, indicated on casts.—Sharpe). Jossil, 14 species. 
Lower and Upper Silurian. North America and Europe. 
