78 
MOLLUSC A. 
ORDER VITI. 
SCUTIBRANCHIATA* 
The Scutibrancliiata comprise a certain number of Gasteropoda, simi- 
lar to the Pectinibrancliiata,in the form and position of the branchiae, 
as well as in the general form of the body, but in which the sexes are 
united, in such a way, however, as to allow them to fecundate them- 
selves. Their shells are very open, withoiit an operculum, and most 
of them without the slightest turbination, so that they cover these 
animals, and particularly their branchiae, in the manner of a shield. 
The heart is traversed by the rectum, and receives the blood from 
two auricles, as is the case in the greater number of bivalves. The 
Halyotis, Lin.-\ 
Is the only genus of this order in which the shell is turbinated ; it is 
distinguished from that kind of shell by the excessive amplitude of 
the aperture, and the flatness and smallness of the spire, which is 
seen from within. This form has caused it to be compared to the 
ear of a quadruped. In the. 
Halyotis, Lam., 
Or the true Halyotes, the shell is perforated along the side of the 
columella by a series of holes; when the last hole is not terminated, 
it gives to that part the look of an emargination. The animal is one 
of the most highly ornamented of all the Gasteropoda. A double mem- 
brane, cut into leaves and furnished with a double range of filaments, 
extends, at least in the most common species, round the foot and on 
to the mouth ; outside its long tentacula, are two cylindrical pedicles 
which support the eyes. The mantle is deeply cleft on the right side, 
and the water, which passes through the shell, penetrates through it 
into the branchial cavity ; along its edges we observe three or four 
filaments Avhich the animal can protrude through these holes. The 
mouth is a short proboscis 
The PadollcE, Month, have an almost circular shell, in which the 
holes are nearly obliterated, and there is a deep sulcus that follows 
the middle of the whorls, and is marked externally by a salient ridge ; 
Padole briquete, Month, II, p. 114. 
* M. de Blainville unites this order and the following one (the Chitones ex- 
cepted) in his sub-class of the Paracephahphora Hermaphrodita. 
-f- The Paracephaloph. Hermaph. Otid., Blainv. 
X All the Halyotides, Gin., except the imperforata and the^errersa. 
This genus, although it has been denied, most certainly has its counterpart 
among the fossils. M. Marcel de Serres has described a species found in the cal- 
careous strata of Montpellier {Hal. Philherti), Ann. des Sc. Nat. tome XII, pi. 
xlv, f. A. 
