MOLLUSKS 147 
The spire of the shell is blunt, and in old individuals its apex 
is apt to be broken off. The surface of the shell is covered with 
seaweed and mud, but 
when cleaned it is seen 
to be black, with a shin- 
ing black interior. This 
snail drills holes through 
the shells of other mol- 
lusks and devours them. 
It is, however, preyed 
upon by young hermit 
crabs, that occupy the 
shells after devouring 
the mollusk itself. 
The Sand-Flat Snail, 
(Nassatrivittata, Fig. 106), 
can be dist in gui she d Fig. 107; Periwinkles clustering upon a rock at 
Annisquam, Mass. 

from Nassa obsoleta by 
its sharp spire, angular suture and regularly granular surface. The 
shell is five-eighths of an inch long, and two sharp-pointed fleshy 
processes arise from the posterior end of the foot giving the impres- 
sion of a pair of tails. There is a pair of long, 
slender tentacles on the head, and half way up 
on the side of each there is an eye. The siphon 
tube is long and curved upward, while the pro- 

boscis is even longer and extends forward as 
a flexible tube. The snail applies this proboscis 
to the surface of other snail shells, bores through 
Fig. 108; PERIWINKLE. 
From life. 
by means of its rasping teeth, and then devours 
the soft parts of the prey. Nassa trivittata 
appears to feed upon every species of mollusk through whose shell 
it is capable of boring, and will readily attack individuals of its 
own species. 
It is found from eastern Florida to Nova Scotia, and is most 
abundant upon sand flats in Long Island Sound, and on the Massa- 
chusetts coast north of Cape Cod. It is also found on muddy or 
stony bottoms and extends into water about 240 feet deep. When 
the tide goes out it crawls slowly over the moist sand leaving a tortu- 
