SUPPLEMENT NO. 4 DATEDAUGUST 14, 1998
                       TO PROSPECTUS DATED OCTOBER 6, 1997
                                   RELATING TO
         $80,000,000 6 1/4% CONVERTIBLE SUBORDINATED DEBENTURES DUE 2004
                    INTEREST PAYABLE FEBRUARY 1 AND AUGUST 1
           AND SHARES OF COMMON STOCK ISSUABLE UPON CONVERSION THEREOF

         All  capitalized  terms  used but not  defined  herein  shall  have the
meanings  set forth in the  Prospectus  dated  October 10, 1997,  as  previously
supplemented (the "Prospectus"), forming a part of the Registration Statement on
Form S-3 (Registration No.  333-35827).  Any cross references in this Supplement
refer to portions of the Prospectus.

           The purpose of this Supplement is to provide  additional  information
regarding   the   Selling   Securityholders.   In   addition   to  the   Selling
Securityholders named in the Prospectus, the following table sets forth the name
of each additional  Selling  Securityholder  and relationship,  if any, with the
Company  and (i) the  amount  of  Debentures  owned by each  additional  Selling
Securityholder  as of August 14, 1998  (subject to the  qualification  set forth
below),  (ii) the  maximum  amount of  Debentures  which may be offered  for the
account of such additional Selling  Securityholder  under the Prospectus,  (iii)
the amount of Common Stock owned by each additional Selling Securityholder as of
August  14,  1998,  and (iv) the  maximum  amount of Common  Stock  which may be
offered for the account of such Selling Securityholder under the Prospectus.






Name of Selling Securityholder  Principal Amount           Principal Amount        Shares of      Shares of Common
                                of Debentures Owned        of Debentures           Common Stock   Stock Offered Hereby (2)
                                                           Offered Hereby          Owned  Prior   
                                                                                   to Offering(1)

                                                                                               
Alpine Associates............      1,500,000              1,500,000                88,889               88,889
Offshore Strategies LTD(4)...      1,220,000                945,000                72,296               56,000
Laterman Strategies 90s LLC(3)       286,600                366,000                16,984               21,689
First Delta Securities.......        300,000                300,000                17,777               17,777
Laterman and Company.........        189,000                189,000                11,200               11,200
Total........................     $3,495,600              $3,300,000                  N/A              195,555
                                  ==========              ==========                  ===              =======
- -----------------------



(1)  Includes the shares of Common Stock into which the Debentures  held by such
     Selling Securityholder are convertible at the initial conversion price. The
     conversion  price and the number of shares of Common  Stock  issuable  upon
     conversion  of the  Debentures  are  subject to  adjustment  under  certain
     circumstances.   See  "Description  of  Debentures  -  Conversion  Rights."
     Accordingly,  the number of shares of Common Stock issuable upon conversion
     of the Debentures may increase or decrease from time to time.

(2)  Assumes  conversion into Common Stock of the full amount of Debentures held
     by  such  Selling  Securityholder  at the  initial  conversion  price.  The
     conversion  price and the number of shares of Common  Stock  issuable  upon
     conversion  of the  Debentures  are  subject to  adjustment  under  certain
     circumstances.   See  "Description  of  Debentures  -  Conversion  Rights."
     Accordingly,  the number of shares of Common Stock issuable upon conversion
     of the  Debentures  may increase or decrease from time to time.  Fractional
     shares will not be issued upon conversion of the Debentures;  rather,  cash
     will be paid in lieu of fractional shares, if any.

(3)  Includes $250,000 aggregate principal amount of freely tradable Debentures.






(4)  Includes $275,000 aggregate principal amount of freely tradable Debentures.

         Because the Selling  Securityholders  may, pursuant to this Prospectus,
offer all or some portion of the Debentures and Common Stock they presently hold
or, with respect to Common Stock,  have the right to acquire upon  conversion of
such Debentures, no estimate can be given as to the amount of the Debentures and
Common Stock that will be held by the Selling  Securityholders  upon termination
of any such sales. In addition, the Selling Securityholders identified above may
have  sold,  transferred  or  otherwise  disposed  of all or a portion  of their
Debentures  and  Common  Stock  since  the  date  on  which  they  provided  the
information  regarding their Debentures and Common Stock, in transactions exempt
from the  registration  requirements of the Securities Act of 1933. See "Plan of
Distribution."

         The Company may from time to time, in accordance with the  Registration
Rights  Agreement,   include  additional   Selling   Securityholders  in  future
supplements to the Prospectus.

         Except as described above, none of the Selling  Securityholders  listed
above had any material  relationship  with the Company other than as a result of
ownership of the Debentures,  within the three-year period ending on the date of
this Prospectus.