1 
392 THE MEDALS OF -CREATION. _ Cuar. XI. 
celled). The casts of these shells often have fissures, pro- 
duced by the decomposition of the septa; and occasionally 
these cavities are occupied by calcareous spar. Specimens 
of this kind commonly split into two parts, in one of which 
two, and in the other three, chambers may be detected ; the 
fifth chamber is the canal of the peduncle. Four species 
are known, and all belong to the Silurian rocks. 
OrtHis, Leprzna, and Propucta form a third family, 
with horizontal spiral arms, unsupported by shelly processes. 
Davidsonia is a Lepteena attached by the ventral valve, and 
the only genus in this family which is fixed by the shell 
itself. 
CatceoLta. A genus of Brachiopoda; the shell of an 
inverted pyramidal form, the upper valve nearly flat; found 
in the Devonian strata of the Eifel, and in Devonshire. 
Crania, Ly. fig. 205. These are small brachiopodous — 
shells, attached to other bodies; very frequently to the 
Echinites of the chalk. The free valve is commonly 
wanting, but I have found specimens dispersed in the rock. 
In many of the quarries in Kent and Sussex, the helmet 
Echinites bear groups of these shells. Ly. jig. 13. 
Orpicuta. This genus resembles Crania in form, the 
upper valve being like a limpet, whilst the attached valve is - 
fiat ; it differs, however, from Crania in being horny and 
flexible, and is fixed to rocks on the bed of the sea, by a 
muscular pedicle passing out through a small fissure. 
Species of Orbicula are found in strata of all ages, from 
the Lower Silurian to the Tertiary, and several are now 
living in tropical seas. 
Osotus. Hichwald. 1n the Lower Silurian (Odolite grit) 
of Sweden and Russia, is a Lingula, with a hinge and a 
notch for the pedicle; it has not hitherto been found in 
Britain. 
