108 CONTRIBUTIONS 
thickened, the callus being reflected at the middle of the 
umbilicus ; umbilicus large, grooved ; whorls four, round- 
ed ; mouth subovate, about three fourths the length of the 
shell. 
Length 5-20ths, Breadth .2, of an inch. 
, 
Observations. In the roundness of the whorls it resem- 
bles the minor described above, but differs in being globose, 
while that shell is more elliptical. It has also a much 
smaller callus. 
N. gibbosa. Plate 4. Fig. 92. 
Description. Shell subovate, gibbous, smooth ; spire 
rather produced; substance of the shell thick; callus 
thick; umbilicus large; whorls five ; mouth sub-elliptical. 
Length 1.1, Breadth .9, of an inch. 
Observations. I have received but a single specimen of 
this species. It is rather more elongated than usual in 
the Natice. The upper part of the whorls being flattened 
and the lower part being inflated, gives the shell a gibbous 
appearance. 
NM. semilunata. Plate 4. Fig. 93. 
Description. Shell subglobose, smooth; substance of the 
shell rather thin ; spire slightly elevated; suture rather 
impressed; columella but slightly thickened, the callus 
being reflected at the middle of the umbilicus ; umbilicus 
large and grooved; whorls five, inflated, slightly flattened 
