ORDER SCUTIBRANCHIATA. 85 
EIGHTH ORDER OF GASTEROPODA. 
SCUTIBRANCHIATA. 
THE scutibranchiata comprise a certain number of gastero- 
poda, similar to the pectinibranchiata in the form and position 
of the gills, 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 themselves. Their shells are very open, 
without an operculum, and for the most part without a trace of 
turbination, so that they cover these animals, and particularly 
the gills, 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. 
* Hatyoris, 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. 
HALYOTIS (proper), Zam., 
Or the true Halyotis. 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 emargina- 
tion. 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 
