Dear Jan,

>The author uses an index to explain the differences between slow and fast
burrowers. E.g. the >genus Donax is given an index of 17, indicating that
this is a very fast burrower.

Vermeij used the burrowing rate index (B.R.I) that was defined by S. M.
Stanley
(1970, Relation of Shell Form to Life Habits in the Bivalvia (Mollusca),
published by
the Geological Society of America). In the page 57, there is an equation to
define
this and the actual data are listed for many species in the Table 6, p.
102-105.
The mean B.R.I. for Donax denticulata is listed as 17. (For D. varabilis,it
is 7).

The index was designed for standardization in the rate for different sizes
of the
same species, so that the specific comparisons are meaningful. The
equation
is a simple one: B.R.I. is the cube root of the mass in grams of the live
shell, divided
by burrowing time in seconds, times 100. By this way, the index can be
nearly constant
for different sizes of the same species. Then, inter-specific comparison can
be made:
if the index number was greater than 6, the bivalve was classified as  $B!H (Jvery  (J
rapid $B!I (J, (J
2 to 5 as  $B!H (Jrapid $B!I (J, 0.6 to 1 as  $B!H (Jmoderately rapid $B!I (J, 0.1 to 0.5  $B!H (Jslow $B!I (J  (J
and less than 0.09
 $B!H (Jvery slow $B!I (J. (Stanley $B!G (Js Table 4, p. 57) (J

The reasoning for this procedure was described in detail in p. 56, but the
above
explanation should be good enough.   Hope this can help the person in need
of
the information.

Masashi Yamaguchi


Masashi Yamaguchi
e-mail: [log in to unmask]
HTTP://www2s.biglobe.ne.jp/~big/coral/
Department of Marine Sciences,
University of the Ryukyus,
1 Senbaru, Nishihara, Okinawa 903-0213  Japan