10 CEPHALOPODA. HAMITES. 
Genus I. — BELLEROPHON. — Montfort. 
Generic Character. — Shell thick, univalve, unilocular, 
involute, umbilicated on both sides ; nearly symmetrical, 
bicarinated, and almost spherical, the last volution envelop- 
ing the others; aperture very large, semilunate, arched, and 
terminated by the extremities of the columella, or axis, 
which is transverse, and provided with a sinus or notch in 
the lip between the keels. 
Bellerophon hiulcus.. Plate II. fig. 14. 
- The shells of this genus are known only in a fossil state, and are character- 
istic of the Carboniferous limestone, and of the strata belonging to the oldest 
secondary formations ; in the latter situation, the shells are frequently changed 
into silex. 
Naturalists have been much puzzi!ed with the species of this genus. They 
have been described by some as chambered shells, and as provided with a 
siphuncle; but Defrance has satisfactorily disproved this opinion. There can 
be no doubt that the animals which inhabited shells of this genus were closely 
allied to those of the Argonautz. Dr Fleming has considered Bellerophon as 
nearly connected with Tornatella, and placed it accordingly after that genus in 
his family Tornatellada. We are, however, convinced, that its proper situa- 
tion in the system is where we have now placed it. . They differ, however, in 
two particulars, viz. in the nearly globular form of the shells, and in being 
very thick ; while those of the genus A7gonauta are very thin. 
The genus consists of two sections, — 
Section 1.— With a mesial band. 
Section 2. — Destitute of a mesial band. 
GRAND DIVISION IlI.—CEPHALOPODA POLYTHALAMA. 
Shell multilocular, either entirely or partly internal, and 
situated on the posterior portion of the body of the animal. 
The fossil shells of this division are very numerous, and widely diffused 
through different strata. 
TRIBE I.— AMMONACEA. 
Septa sinuous, lcbed and cut at the margin, and meeting 
together upon the inside of the shell, where they are articu- 
lated by serrated sutures, furnished with a siphuncle, which 
penetrates through the whole of the partitions or septa. 
In all the genera of this family, the chief variation consists in the external 
form of the shells; the internal structure of the whole being similar, and in- 
tended as a float, subservient to the animal inhabitants. 
Genus Il. —HAMITES — Parkinson. 
Generic Character — Shell fusiform, cylindrical, hooked 
or bent into-two parallel limbs, recurved at the posterior 
extremity ; exteriorly undulated ; chambered, with the 
