TUSK-SHELLS. 207 
cesophageal cerebral ganglions, and completeness 
of the circulation, it has established its claims as a 
Gasteropod. There are also traces of alliance with 
some of the inferior classes. The red blood and 
vermiform configuration of the posterior part of the 
animal show some of the characters of the Anne- 
lida.” 
Two species of the genus 
are recognised as British, D. 
entalis, the Smooth Tusk, and 
D. Tarentinum, the Grooved 
Tusk. Of these the former is 
common around the shores of 
Scotland and the north of Eng- 
land; the latter on our southern 
coasts. Though possessing much 
resemblance to each other, they 
may be distinguished by the 
small end of the latter being 
finely grooved lengthwise, while | 
the former is quite smooth and | 
shining 
The Smooth Tusk, here re- 3 
presented, grows to a length of 4 
nearly two inches, with a dia- 
meter of about a quarter of an 
inch at the larger end. It is 
opaque, of a shining white sur- 
face, like porcelain, never tinged 
(asits southern congener usually 
is) with pink, and never marked 
with sculpture, but often with IX 
rings indicating the progress Of pewratium TARENTINUM, 
growth. (magnified). 
It is a deep-water species, living “ buried in sand 
pMjreifl p)))NH yy 
