220 ASPIDOBRANCHIA. PATELLADZ. 
underneath. Foot oval. Termination of the anus and oviduct 
on the right side at the base of the neck. Heart situated on 
the left side of the upper part of the neck. 
General Observations on this Family. 
When the animal is carefully extracted from the shell, and 
is viewed from above, the dilated part of the mantle is seen ex- 
tending equally round the whole animal. Above the base of 
the mantle, and arising from the upper margin of the foot, is 
a broad many-lobed muscle extending round the posterior part 
of the animal, and is produced anteriorly as far as the sides of 
the pericardium, where it becomes abruptly and extremely nar- 
row. This muscle attaches the animal to the shell, which bears 
the impression of all its lobes. The upper part of the animal 
is covered by a membrane, which is perhaps a dilatation of the 
mantle. It is attached on every side by the circular muscle 
mentioned above. On removing this membrane, the upper 
part of the neck, the terminations of the oviduct and anus on 
the right, the heart within the pericardium on the left, and the 
dorsal aspect of the abdomen filled with the liver, and the in- 
testines convoluted in its substance, may be readily seen. 
To obtain a view of the lower aspect of the interior of the 
body, it is necessary to separate the foot carefully from its at- 
tachment to the circular muscle, and to divide longitudinally 
the lower aspect of the neck. We can then observe the ros- 
triform mouth, at the base of which is seen the nervous cord 
passing upwards to form the nervous collar round the cesopha- 
gus. In the abdominal cavity to the nght anteriorly, is situa- 
ted the spiral tongue and the ovarium, between which and the 
tongue the intestines are very evident, when the ovarium is 
not in a distended state; in which case they are often com- 
pletely hidden. 
The nervous cord above mentioned forms on each side, in the 
region of the tentacles, a somewhat bilobate ganglion which re- 
ceives three nerves; one from the eye, one from the tentacles, 
and the third from the surrounding integuments. 
Such are the characters common to the two following genera 
of animals, both of which inhabit our seas. 
