GASTEROPODA TUBULIBRANCHIATA. 269 



Magilus, Montf. 



The Magili have a longitudinally carinated tube, which is at first regularly 

 spiral, and then extends itself in a line more or less straight; although the 

 animal is unknown, it is higlily probable that it should be placed near the 

 Vermeti. The 



SlLIQUARIA, Brug. 

 Resembles Vermelus in the head, the position of the operculum, and in the 

 tubular and irregular shell; but there is a fissure on the whole length of this 

 shell which follows its contour, and which con'esponds to a similar cleft in 

 that part of the mantle which covers the branchial cavity. Along the whole 

 side of this cleft is a branchial comb, composed of numerous, loose and tab- 

 ular-like lamellae. 



ORDER VIII. 



SCUTIBRANCHIATA. 



The Scutibranchiata comprise a certain number of Gasteropoda, 

 similar to the Pectinibranchiata, in the form and position of the 

 branchiae, as well as in the general form of the body. Their shells 

 are very open, without an operculum, and most of them without the 

 slightest turbination, so that they cover these animals, and particu- 

 larly their branchise, in the manner of a shield. The 



Halyotis, Lin. 



Is the only genus of this order in which the shell is turbinated; it is distin- 

 guished 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 

 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 membrane, cut into leaves and furnished 

 with a double range of filaments, extends, at least in the most common spe- 

 cies, 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 obseiTe three or 

 four filaments which the animal can protrude through these holes. The 

 mouth is a short proboscis. 



