ImportError: No module named 'crud.urls'を解決できません。

###前提・実現したいこと
crudアプリのテンプレートを表示したいです。

###発生している問題・エラーメッセージ

Performing system checks...

Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0x7f55e774a598>
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/django/utils/autoreload.py", line 226, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/runserver.py", line 121, in inner_run
    self.check(display_num_errors=True)
  File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 374, in check
    include_deployment_checks=include_deployment_checks,
  File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 361, in _run_checks
    return checks.run_checks(**kwargs)
  File "/usr/local/lib/python3.4/dist-packages/django/core/checks/registry.py", line 81, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/usr/local/lib/python3.4/dist-packages/django/core/checks/urls.py", line 14, in check_url_config
    return check_resolver(resolver)
  File "/usr/local/lib/python3.4/dist-packages/django/core/checks/urls.py", line 24, in check_resolver
    for pattern in resolver.url_patterns:
  File "/usr/local/lib/python3.4/dist-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/usr/local/lib/python3.4/dist-packages/django/urls/resolvers.py", line 313, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/usr/local/lib/python3.4/dist-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/usr/local/lib/python3.4/dist-packages/django/urls/resolvers.py", line 306, in urlconf_module
    return import_module(self.urlconf_name)
  File "/usr/lib/python3.4/importlib/__init__.py", line 109, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 2254, in _gcd_import
  File "<frozen importlib._bootstrap>", line 2237, in _find_and_load
  File "<frozen importlib._bootstrap>", line 2226, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1200, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1129, in _exec
  File "<frozen importlib._bootstrap>", line 1471, in exec_module
  File "<frozen importlib._bootstrap>", line 321, in _call_with_frames_removed
  File "/home/ubuntu/workspace/c9_django/urls.py", line 22, in <module>
    url(r'^crud/', include('crud.urls', namespace='crud')),  # 追加する
  File "/usr/local/lib/python3.4/dist-packages/django/conf/urls/__init__.py", line 50, in include
    urlconf_module = import_module(urlconf_module)
  File "/usr/lib/python3.4/importlib/__init__.py", line 109, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 2254, in _gcd_import
  File "<frozen importlib._bootstrap>", line 2237, in _find_and_load
  File "<frozen importlib._bootstrap>", line 2224, in _find_and_load_unlocked
ImportError: No module named 'crud.urls'

初歩的なところで恐縮です。。。

###該当のソースコード
【c9_django/setting.py】

import sys
sys.path.append('/path/to/crud')
import crud
import os
・・・
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'crud',  # 追加する
]
・・・
TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join(BASE_DIR, 'templates'),],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

【crud/view.py】

from django.shortcuts import render
from django.http import HttpResponse


def index(request):
    return render(request, 'crud/index.html', {})


def add(request):
    return render(request, 'crud/edit.html', {})


def edit(request, editing_id):
    return render(request, 'crud/edit.html', {})


def delete(request):
    return HttpResponse('Delete')

【curd/crud/urls.py】

from django.conf.urls import url
from django.contrib import admin
from . import views

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^$', views.index, name='index'),
    url(r'^add/$', views.add, name='add'),
    url(r'^delete/$', views.delete, name='delete'),
    url(r'^edit/(?P<editing_id>\d+)/$', views.edit, name='edit'),
]

【c9_django/urls.py】

from django.conf.urls import url
from django.contrib import admin
from django.conf.urls import include, url

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^crud/', include('crud.urls', namespace='crud')),  ★ここです。
]

実際は,c9_djangoと同ディレクトリにindex,add,delete,editテンプレートを用意しています。
【c9_django/urls.py】のurlpatternsの２行目を外すとエラーがなくなるのですが、ここまでしかわかりませんでした。。。。

ご経験ある方、ご教示ください。

###補足情報(言語/FW/ツール等のバージョンなど)
python 3.4.3
django '1.10.6'