<?php
$page = (get_query_var('paged')) ? get_query_var('paged') : 1;
query_posts("paged=$page");
?>
<?php $the_query = new WP_Query('post_type=portfolio&showposts=4&orderby=desc'); ?>
<?php while ($the_query->have_posts() ) : $the_query->the_post(); ?>
<?php
$thumb_id = get_post_thumbnail_id();
$thumb_url = wp_get_attachment_image_src($thumb_id,'', true);
?>
<div><?php the_title(); ?></div<>
<?php endwhile; ?>
<div class="pages">
<ul>
<?php if (function_exists("pagination")) {
pagination($custom_query->max_num_pages);
} ?>
</ul>
</div>
<?php wp_reset_postdata(); ?>
// archive-portfolio.php
<?php while (have_posts() ) : the_post(); ?>
<?php
$thumb_id = get_post_thumbnail_id();
$thumb_url = wp_get_attachment_image_src($thumb_id,'', true);
?>
<div><?php the_title(); ?></div<>
<?php endwhile; ?>
<div class="pages">
<?php the_posts_pagination() ?>
</div>