Fortran -> C Interop w/ Argument Errors

All,

In my continuing journey in learning how to interoperate Fortran with C, I've come across yet another confusing situation. Below, I'm trying to pass two REAL data arrays to a C routine gpc _cvlist to populate a data structure with the data in the arrays but when I compile, I get the error #6633: The type of the actual argument differs from the type of the dummy argument.   [XV] & [YV] . I'm not understanding why this error would occur since I (thought)  was consistent with my declarations concerning the two arrays.

Below is the code:

!  F2CGPCList.f90
!
!  FUNCTIONS:
!  F2CGPCList - Entry point of console application.
!

!****************************************************************************
!
!  PROGRAM: F2CGPCList
!
!  PURPOSE:  Entry point for the console application.
!
!****************************************************************************

    module gpc_list
	   use, intrinsic :: ISO_C_BINDING
	   implicit none
	   private
	   public C_GPC_VERTEX, C_GPC_VERTEX_LIST, C_GPC_POLYGON
       public gpc_cvlist

	   TYPE, BIND(C) :: C_GPC_VERTEX
	      REAL(C_DOUBLE) :: x
	      REAL(C_DOUBLE) :: y
	   END TYPE C_GPC_VERTEX

	   TYPE, BIND(C) :: C_GPC_VERTEX_LIST
	      INTEGER(C_INT) :: num_vertices
	      TYPE(C_PTR) :: C_vertex
	   END TYPE C_GPC_VERTEX_LIST

	   TYPE, BIND(C) :: C_GPC_POLYGON
	      integer(C_INT) num_contours
	      type(C_PTR) hole
	      type(C_PTR) C_contour
	   END TYPE C_GPC_POLYGON

	   interface

!*********************************************************************
!                   GPC FUNCTION ADD-ONS
!
	      SUBROUTINE gpc_cvlist(npoly, px, py, vertex_list, iret) &
	         BIND(C,name='gpc_cvlist')
	         IMPORT :: C_INT, C_FLOAT, C_GPC_VERTEX_LIST
             implicit none
 	         integer(C_INT),    intent(inout) :: npoly
 	         integer(C_FLOAT),  intent(inout) :: px(*)
 	         integer(C_FLOAT),  intent(inout) :: py(*)
	         TYPE(C_GPC_VERTEX_LIST) vertex_list
 	         integer(C_INT),    intent(inout) :: iret
	      end SUBROUTINE gpc_cvlist

	   end interface

	end module gpc_list


    program F2CGPCList

    use GPC_List

    use, intrinsic :: ISO_C_BINDING

    implicit none

    ! Variables
! - - - local declarations - - -
  INTEGER :: nverts,ii,ier

  REAL    :: xv(10),yv(10)

  type(C_GPC_VERTEX_LIST) C_verticies

    ! Body of F2CGPCList
  WRITE (*,*) "The following are the polygon points to be xfered "

  nverts = 10
  DO ii = 1,nverts
    xv(ii) = float(ii*10)
    yv(ii) = float(ii*10+1)
    write(*,*)'x/yv = ',ii,xv(ii),yv(ii)
  END DO

  CALL gpc_cvlist( nverts, xv, yv, C_verticies, ier )

  end program F2CGPCList

#include "gpc.h"

#define	G_MALLOC(p,type,np,str)  { if ((np) > 0) { \
		(p)=(type*)malloc((np)*sizeof(type)); \
		if (p==((type*)NULL)) { \
		    fprintf(stderr, "malloc failure: %s\n", (str) ); \
		  } \
		} \
		else \
		    (p)=(type*)NULL; \
		}

void gpc_cvlist ( int npoly, float *px, float *py,
				gpc_vertex_list *contour, int *iret )
/************************************************************************
 * gpc_cvlist                                                           *
 *                                                                      *
 * This function generates a GPC vertex list structure given a set of	*
 * polygon points.							*
 *                                                                      *
 * gpc_cvlist ( npoly, px, py, contour, iret )				*
 *                                                                      *
 * Input parameters:                                                    *
 *      *npoly  	int             Number of points in polygon	*
 *      *px     	float[]         X array				*
 *      *py     	float[]         Y array				*
 *                                                                      *
 * Output parameters:                                                   *
 *      *contour  	gpc_vertex_list Vertex list structure		*
 *      *iret   	int     	Return code                     *
 *                                                                      *
 **                                                                     *
 ***********************************************************************/
{
int	ii;
/*---------------------------------------------------------------------*/

    *iret = 0;

    contour->num_vertices = npoly;

    G_MALLOC ( contour->vertex, gpc_vertex, npoly, "gpc_vertex creation" );

    for ( ii = 0; ii < npoly; ii++ )  {
	contour->vertex[ii].x = px[ii];
	contour->vertex[ii].y = py[ii];
    }

    return;

}

Thanks in advance,

Jeff