CRANIA. 
Prats I. 
Genus CRANIA, Retzius. 
Testa inequivalvis, equilateralis, orbicularis, posticé sub- 
truncato-quadrata, interdum laevigata, interdum ru- 
gosa, valvd inferiore adherente, incrassatd, intus varie 
cicatricosd, rostello centrali, superiore convexd, inter- 
dum depress, vertice subcentrali. Ligamentum aut 
cardo nullum. 
Shell inequivalve, equilateral, orbicular, posteriorly some- 
what truncately squared, sometimes smooth, some- 
times roughened, lower valve adhering, thickened, 
internally variously scarred, with a central rostellum, 
upper valve convex, sometimes depressed, vertex 
nearly central. No ligament or hinge. 
The shell of this Brachiopod was first known in a fossil 
state. The calcifying functions of the animal are exer- 
cised chiefly by the under lobe of the mantle for the secre- 
tion of a thickened adherent valve, unconnected by any 
hinge or ligament with the upper valve; and before the 
time of Linnzeus it was named Nummus, and sometimes 
Nummulus, Brattenburgensis, “ Brattenburgh Money.” Lin- 
neus and Chemnitz still confounded recent and fossil 
specimens together ; and the separation of the valves led 
naturalists, among whom were Miiller and our own Mon- 
tagu, to describe them as Limpets. A curious character 
in the adherent valve of this genus, and which seems to 
have attracted the attention of Linnzus, is a similitude, in 
the configuration of the internal muscular scars and pro- 
tuberances, of a human face. A little above the centre a 
raised callosity, termed the rostellum, forms the nose, and 
the scars of the two posterior adductor muscles of the 
animal give the resemblance of a pair of eyes, while the 
anterior thickened rim serves for the outline of the cheeks 
and chin. This fanciful representation suggested to Lin- 
neus the name Anomia craniolaris; and Crania was soon 
proposed by Retzius to separately distinguish the group. 
M. Defrance described several fossil species of Crania. 
The first special monograph of the genus, which included 
the recent species, was made in 1828 by M. Heninghaus, 
of Crefeld. Since that period the Cranié have been ably 
studied by Sowerby, Deshayes, Davidson, and Suess, and 
although little has been added to our knowledge of the 
species, some interesting particulars have been collected of 
their geographical and bathymetrical distribution and its 
bearings on geological phenomena. Only four recent spe- 
cies have been collected. C. anomala, of our own coast, 
the best-known species of the genus, ranges from Spitz- 
bergen, in the north of Europe, to Vigo Bay, in the south ; 
but here it stops. Professor Suess has observed that C. 
anomala ranges over this area closely, both in locality and 
depth, with Terebratulina caput-serpentis. Wherever one 
genus is found between Spitzbergen and Vigo the other is 
found also; but the C. anomala does not pass with the 7. 
caput-serpentis into the Mediterranean nor to North Ame- 
rica; and he deduces some interesting conclusions from 
this fact in connection with their fossil distribution to show 
the relations of their existence in time as well as in space. 
Another species, C. tabinata, appears in the Mediterranean, 
and it was dredged in the Aigean by Professor Forbes, 
from depths varying between forty and a hundred and fifty 
fathoms. A third species, C. rostrata, is recorded from 
West Africa; and a species, which I have had the pleasure 
of naming ©. Suessii, was collected by Mr. Strange in 
Australia. No Crania has, as yet, been collected in the 
New World. C. radiosa, described by Dr. Gould from a 
shell received from Rio Janeiro proves to be an Ordicula 
(Discina, nonuul.), which genus is not uncommon in the 
waters of South and Central America. 
In Terebratula and Rynchonella the natural position of 
the mollusk is to repose upon its back; the lower valve of 
the shell is the dorsal valve, and the upper or ventral 
valve, from which anchorage is obtained, projects over one 
side, like a beak, for lowering the anchor. In Crania the 
position of the mollusk is reversed, the ventral valve is 
undermost ; and, having no need, or even space, for a ten- 
dinous anchor, the valve becomes agglutinated at once to 
the place of attachment. But it will be observed, that in 
the genus Orbicula the shell is not so closely adherent, and 
there is a tendinous muscle of attachment passing through 
a fissure in a disk of the under valve; and itis conjectured 
that the same thing obtains in a rudimentary form in 
Crania in an early stage of its development. 
or brachial appendages, of Crania have no internal apo- 
physary skeleton for their support ; they are folded into a 
pair of spiral coils, which are directed towards the conca- 
vity of the upper valve, a limpet-like plate, and they are 
supported in the concavity of the upper valve by a central 
prominence rising up between them from the lower. This 
central prominence is termed the rostellum. The under 
valve of Crania, as with other adherent shells, varies much 
in thickness according to the nature of its place of attach- 
ment. 
The arms, 
June, 1862. 
