78 MOLLUSC A. 



ORDER VIII. 



SCUTIBRANCHIATA*. 



The Scutibranchiata comprise a certain number of Gasteropoda, simi- 

 lar to the Pectinibranchiata, 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, without 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, Lzw.f 



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 which the animal can protrude through these holes. The 

 mouth is a short proboscis J. 



The Padollce, Montf., 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, Montf., II, p. 114. 



* M. de Blainville unites this order and the following one (the Chitones ex- 

 cepted) in his sub-class of the Paracephalophora Hermaphrodila. 



f The Paracephaloph. Hermuph. Otid., Bluinv. 



J All the Halyotides, Gm., except the imperforata and the perversa. 



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. Philberti), Ann. des Sc. Nat. tome XII, pi. 

 xlv, f. A. 



