MOLLUSCA. 
345 
Mollusca. In form, the genus Lenrrcurma is nearly related to the structure similar to the ammonites, the inner walls being Mollusca. 
\e\—= former. The margin of the mouth reaches to the centre articulated with sinuous sutures, and the partitions perfor- —-~ 
of the shell on both sides, and the partitions are destitute 
ofasyphon. Lamark is in possession of a recent shell of 
this species from the sea near Teneriff. 
The shells which Mr. Sowerby, in his Mineral Concho- 
logy, has figured under the genus Exiresouitues, have the 
whorls conspicuous, although the mouth clasps the body 
whorl. But it is easily distinguished from the other genera 
with which it is related by its elliptical form. 
The genus Discorsts of Lamark (formerly called by him 
Planulites) bears a considerable resemblance to the nauti- 
lus in form, but the whorls are all apparent, and the parti- 
tions entire. 
In the genus Roraxra, the spires approach to a conical 
shape, and the marginated trigonal aperture is reflected to- 
wards the base of the shell. It consists of shells which are 
now found in a fossil state. 
The nautilus spirula of Linnzeus has afforded characters 
for the construction of anew genus termed Sprruta. The 
whorls are separate, the mouth orbicular, the partitions per- 
forated by a tube, and the last turn of the spire prolonged 
in astraight line. This last character was unknown to Lin- 
nus, whe had only seen the spiral body of the shell. 
The genus Srrroxmva has the last turn of the spire pro- 
duced like the preceding, but the whorls are contiguous. 
The partitions are perforated by a tube. 
The genus Lrrvota is allied to the spirula and spirolina 
in the production of the last whorl. The spires of the body 
are contiguous, and the partitions are pierced by a number 
of holes. 
In the preceding: genera the inner walls of the cavity are 
simple ; but in the two following, the walls are formed into 
joints by sinuous sutures. The first of these is the AMmo- 
NITES, including those shells which have been termed cor- 
nua ammonis. The origin of this name is, by some, sought 
for in their resemblance to the horns of a ram; by others, 
to their having been found near the temple of Jupiter Am- 
mon in Upper Egypt. By the Indians, the ammonites 
sacer is considered as a metamorphosis of the god Vishnu, 
and termed by them salgram or salgraman. It is found 
among the peebles of the Gandica where it joins the Gan- 
ges. In this genus the whorls are contiguous, spiral, de- 
pressed, and obvious. 
The Orsuires of Lamark differs from the ammonites 
in the circumstance of the last whorl embracing and con- 
cealing the others. In both the syphon is marginal. 
Nearly allied to the preceding is the Turriites of 
Montfort. It is similar in internal structure, but while the 
shells of the former are spirally discoid, those of the present 
genus are spirally turreted, resembling a Turbo or Turri- 
cula. Several species are figured by Sowerby in his Mine- 
ral Conchology. 
The genus Scapurrss; formed by Parkinson, possesses 
very peculiar characters. It commences with a depressed 
yolution, the last turn of which, after being enlarged and 
elongated, is diminished and reflected inwards. 
2. Multilocular testacea with the shell produced. It 
must be confessed, that the genera of this section are but 
imperfectly understood. The recent kinds are too small to 
admit of any investigation of the anima!, so that we are 
left entirely to conjecture. 
The genus Hiprurrres is of a conical form, and either 
straight or crooked. Within it is transversely chambered, 
and furnished with two lateral, longitudinal, obtuse, con- 
vergingridges. The last chamber is closed by an operculum. 
In the Orrmocera the shell is straight or slightly bent, 
and conical. The chambers are distinct, and pierced with 
a tube. We possess on our shores many minute species of 
this genus- 
The genus Bacurirzs of Faujas St. Fond possesses a 
VOL. Xv. 
ated The shell is fusiform or bent into two parallel limbs. 
Mr. Parkinson has contributed greatly to our knowledge of 
this genus, and has termed it Hamites. We prefer the name 
of the original discoverer to that of our English naturalist, 
which is very faulty. For, according to Pliny, “ Hammites 
ovis piscium similis est.” 
In the Brexemntres the shell is straight, conical, pointed, 
solid at the summit, and furnished with a lateral gutter. 
There is seldom more than one of the cells apparent, of a 
conical form, the older ones having been effaced in succes- 
sion. The genus Tulaxodes of Guettard is not, perhaps, 
entitled to be considered as distinct. 
The Ampiexus of Sowerby belongs to this division. It 
is nearly cylindrical, divided into chambers by numerous 
transverse septa, which embrace each other with their re- 
flected margins. It contains one species from the limestone 
rocks of Ireland, but we may add that it has been supposed 
to belong to the zoophytes rather than the mollusca. 
3. Multilocular testacea of a globular. form. The first 
genus of this section is the Mizrona. The shell is com- 
posed of three or four oval cells, turning round an axis pa- 
rallel to their longest diameter. Many recent species of 
this genus are common on our shores; they were included 
by Montagu in his genus vermiculum. 
In the Renunina the cells are narrow, linear, unilateral, 
curved into a part of a circle, and all situate on the same 
plane. The smallest cell forms a little arch round a mar- 
ginal axis, and the others are placed contiguous to this on 
the same side. The species are all fossil. 
The GyroGona was for many years viewed as a shell of 
a spheroidal form, composed of linear, curved, grooved, 
pieces, terminating in two poles, the external surface obliquely 
spiral, the spires terminating at each pole, and as found only 
in a fossil state. But more recent observations have con- 
nected it with the seed vessel of the genus chara. 
The shells of the genus NuMMULITEs are remarkable for 
their lenticular form. The external surface is smooth, and 
the cells concealed, but internally the transverse shells are 
disposed in a spiral discoid form. The cells are imperfor- 
ate; they are the camerinz of Bruguiére, the helecites of 
Guettard, and the discolithes of Fortis. This last author 
supposes, that they are formed in the interior of an animal 
analogous to the sepia. The same opinion may, with pro- 
priety, be entertained of many other genera of multilocular 
testacea. Faujas St. Fond found a recent specimen of a 
nummulite among the fragments of the corallina officinalis, 
brought from the island of Corsica. 
It. is probable that the genus Lacrna, formed from the 
serpule lagene of Walker’s Testacea minuta Rariora, be- 
longs to the multilocular testacea; as in some of the species 
we have observed the appearances of internal divisions. 
As connected with this division of the Linnzean genera, 
we may take notice of the British shell called by Lightfoot 
Nautilus lacustris, (Phil. Trans. \xxvi. tab. 1). The very 
circumstance of its being a fresh water shell, distinguishes 
it sufficiently from all those which we have been consider- 
ing, and its other characters are likewise peculiar. The 
partitions are distant, and consist of three testaceous plates, 
not united, which leave a sufficient opening between them 
to allow the animal to protrude and withdraw itself: It con- 
stitutes a distinct genus, which has been termed SEGMEN- 
TiNA, from the trivial name bestowed on it by Solander, 
which refers to the structure of the septa. Its place in the 
system is next to the genus planorbis. 
These genera of multilocular shells which we have enu- 
merated, are those which have been established with the 
greatest attention. Many other genera might have been 
enumerated, particularly those formed by Montfort, but the 
character given of them by Cuvier will satisfy the curiosity 
2x 
