218 PERMIAN FOSSILS. 
The reader is referred to M. Deshayes’s Monograph of Dentalium, and to a paper 
by Mr. W. Clark,! for an account of the mollusk of this genus. 
DENTALIUM SorsBil, King. 
INagnosis—Smooth ; curved; gradually tapering. 
The above is a provisional description of a species supposed to be of the present 
genus. It was discovered by Mr. Henry Clifton Sorby, F.G.8., who has only succeeded 
in finding a single specimen, which is not quite perfect at the small end. The specimen 
appears to have been about five eighths of an inch in length; and its curvature is about 
the same as a circle, the radius of which is from half to five eighths of an inch. : 
Dentalium Sorb1i occurs at Connigsborough, near Doncaster. 
Class CEPHALOPODA, Cuvier, 1798. 
CrpHaLopHora, Blainville. 
Diagnosis.—“ A class of molluscous invertebrate animals, in which the head is 
situated between the trunk and the feet, or principal organs of locomotion.” (Owen.’) 
“The Cephalopods have been divided into two sections, depending on their having 
two, or four gills: those with two gills are termed Dibranchians, and such as have four, 
are called Tetrabranchians. The Calamary, Cuttle-fish, Argonaut, and Spirula are 
examples of the dibranchiate, and the Pearly Nautilus represents the tetrabranchiate 
section.”* The latter is the only division known as having representatives in the 
Permian system. 
Order TETRABRANCHIATA, Owen. 
This group contains at least two families, Vautilide and Ammonitide, both con- 
sisting of chambered shells; but the former has the septa or partitions, separating 
the chambers, generally plain at the margins, and perforated centrally or sub-marginally ; 
whereas the latter has the plates variously lobed at the margins, and perforated 
marginally at the medio-dorsal line of the shell. 
Family Nauritipe (Nautilles, restricted), Cuvier. 
Diagnosis.—“ Shell external, spiral, or straight; septa smooth and simple; the last 
' Annals and Magazine of Natural History, 2d series, vol. iv, p. 321. 
2 Cyclopedia of Anatomy, vol. 1, p. 517. 
3 Vide the author’s paper entitled “An attempt to classify the Tetrabranchiate Cephalopods,”’ in the 
Ann. and Mag. of Nat. Hist.,’ vol. xiv, p. 272. 
