THE SMALLER SEA-SHELES 201 
sharply angled, quite in contrast with those of the 
next species. 
Monoceros lapilloides, Conr., the 
Pebbly Unicorn, Figure 211, has a 
pretty little shell, about an inch in 
length, with a spire of four whorls, a 
rather small aperture within which 
are several knobs, or teeth. It is well 
named for it distinctly resembles a 
rolled pebble of granite, and the word 
‘‘Japilloides’?’ means ‘‘like a little stone.’’ 
Monoceros lugubre, Sby., the Sad Unicorn, is 
found in the extreme southern limit of our terri- 
tory, though its home is on the west coast of 
Mexico. It has a thick, heavy shell, about an inch 
long. The wall of the aperture is of a brown color, 
and is marked with several rows of white tu- 
bereles. The little horn near the canal is very 
distinct. 
It is now our pleasant task to consider a few 
species of pure white shells, regularly marked 
with frequent varices. All of them are quite rare, 
but if you search along the shore you will probably 
have the good fortune to find one or more of them. 
The first one is shown in Figure 
212, and is named Scala borealis, Gld., 
(Opalia borealis), the Northern Opal- 
shell. It consists almost wholly of a 
long spire composed of about eight 
whorls, each of which is crossed by 
eight blunt ridges, or varices. The 
aperture is entire, and the rounded 
lips are sometimes stained by the rich Fig. 212 
