492 MOLLUSCA. 
the left side, arises an oblong membranous expansion, on the inferior 
margin of which, about midway, are two thin, circular lamelle, at- 
tached obliquely. On the right side, corresponding to the membra- 
nous expansion or natatory, comes off horizontally an arm, having a 
spatulate extremity facing the proboscis at right angles with the arm, 
and furnished at the elbow with a minute spine. This seems to 
answer the purpose of an operculum. At the junction of the proboscis 
with the natatory above, is the anal orifice. Just below this, on the 
right side, is a bilobed, sacculate organ, communicating by a small 
duct with internal viscera (probably generative). ‘The mouth con- 
nects with an ample cesophagus, to which succeeds an intestinal 
canal, whose course is very apparent, as far as a small, ovate body 
near the spire of the shell, which is the heart, and is seen to pulsate 
very regularly when the animal displays itself. The mantle is folded 
so as to form an ample collar embracing the body, and completely 
encloses the animal when it is withdrawn. Colour faint purplish, 
tinted lake-red.  [s. P. c.] 
The sHELL is nautiloid, ovate, very faintly umbilicate on the left 
side, of about three whorls; the lip of the aperture convex in pro- 
file, the aperture itself narrow elliptical, acute at extremities. It has 
a thin, broad, membranous carina at the angle of the shell. Colour 
violaceous, especially on the spire. 
Obtained in the equatorial Atlantic. 
This appears to be closely allied to A. Lesweurt, as figured in the 
Voyage of the Bonite, pl. 20, f. 1-15, though it differs in several re- 
spects. It was figured by Mr. Dana, and described from his figure 
and notes. I think it quite probable that the point at the junction of 
the foot and neck, considered as an anal opening, may really be the 
ganglion described in the next species, as seated at that part. 
Figure 597, shell and animal, enlarged, with details natural size. 
ATLANTA CUNICULA (Gould). 
T. fragilissima, pellucida, nautilordea, sub-circularis, compressa, carina 
latissima cincta: apertura elliptica, acutangularis. 
